https://www.luogu.com.cn/record/78837222

不开 O2 会超时，求卡常或者求求管理员加上 O2 标签QAQ

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
#include<cassert>
#define siz(x) int((x).size())
#define cauto const auto
#define all(x) (x).begin(),(x).end()
class fastIO{private:char ibuf[50007],*p1=ibuf,*p2=ibuf,obuf[50007],*p3=obuf,sta[50];bool file_end=false;char get(){return p1==p2&&(p2=(p1=ibuf)+fread(ibuf,1,50007,stdin),p1==p2)?(file_end=true),char(EOF):*p1++;}void put(const char x){p3-obuf<50007?*p3++=x:(fwrite(obuf,p3-obuf,1,stdout),p3=obuf,*p3++=x);}public:explicit operator bool(){return!file_end;}size_t flush(){size_t f=fwrite(obuf,p3-obuf,1,stdout);p3=obuf;*p3=0;return f;}fastIO&operator>>(char&t){for(t=get();!isgraph(t);t=get());return*this;}template<typename any>typename std::enable_if<std::is_same<any,char>::value,any>::type tpval(){char t;for(t=get();!isgraph(t);t=get());return t;}fastIO&operator>>(char*t){char c;for(c=get();!isgraph(c);c=get());for(;isgraph(c);c=get())*t=c,t++;*t=0;return*this;}fastIO&operator>>(std::string&t){t.clear();char c;for(c=get();!isgraph(c);c=get());for(;isgraph(c);c=get())t+=c;return*this;}template<typename any>typename std::enable_if<std::is_same<any,std::string>::value,any>::type tpval(){std::string t;char c;for(c=get();!isgraph(c);c=get());for(;isgraph(c);c=get())t+=c;return t;}template<typename any>typename std::enable_if<(std::is_signed<any>::value&&std::is_integral<any>::value&&!std::is_same<any,char>::value)||std::is_same<any,__int128_t>::value,fastIO>::type&operator>>(any&t){t=0;bool y=0;char c=get();for(;!isdigit(c);c=get())if(c==45)y=true;for(;isdigit(c);c=get())t=t*10+c-48;if(y==1)t=-t;return*this;}template<typename any>typename std::enable_if<(std::is_signed<any>::value&&std::is_integral<any>::value&&!std::is_same<any,char>::value)||std::is_same<any,__int128_t>::value,any>::type tpval(){any t=0;bool y=0;char c=get();for(;!isdigit(c);c=get())if(c==45)y=true;for(;isdigit(c);c=get())t=t*10+c-48;if(y==1)t=-t;return t;}template<typename any>typename std::enable_if<(std::is_unsigned<any>::value&&std::is_integral<any>::value&&!std::is_same<any,char>::value)||std::is_same<any,__uint128_t>::value,fastIO>::type&operator>>(any&t){t=0;char c=get();for(;!isdigit(c);c=get());for(;isdigit(c);c=get())t=t*10+c-48;return*this;}template<typename any>typename std::enable_if<(std::is_unsigned<any>::value&&std::is_integral<any>::value&&!std::is_same<any,char>::value)||std::is_same<any,__uint128_t>::value,any>::type tpval(){any t=0;char c=get();for(;!isdigit(c);c=get());for(;isdigit(c);c=get())t=t*10+c-48;return t;}template<typename any1,typename any2>fastIO&operator>>(std::pair<any1,any2>&t){return*this>>t.first>>t.second;}template<typename any1,typename any2>std::pair<any1,any2>tpval(){return std::pair<any1,any2>(tpval<any1>(),tpval<any2>());}template<typename any>fastIO&read(any&t){return*this>>t;}fastIO&read(char*t){char c;for(c=get();!isgraph(c);c=get());for(;isgraph(c);c=get())*t=c,t++;*t=0;return*this;}template<typename any,typename...args>fastIO&read(any&t1,args&...t2){return(*this>>t1).read(t2...);}fastIO&operator<<(const char t){put(t);return*this;}fastIO&operator<<(const char*t){for(;*t;t++)put(*t);return*this;}fastIO&operator<<(const std::string&t){for(const char it:t)put(it);return*this;}template<typename any>typename std::enable_if<(std::is_signed<any>::value&&std::is_integral<any>::value&&!std::is_same<any,char>::value)||std::is_same<any,__int128_t>::value,fastIO>::type&operator<<(any t){if(!t){put(48);return*this;}int len=0;if(t<0)t=-t,put(45);while(t)sta[len++]=char(t%10+48),t/=10;while(len--)put(sta[len]);return*this;}template<typename any>typename std::enable_if<(std::is_unsigned<any>::value&&std::is_integral<any>::value&&!std::is_same<any,char>::value)||std::is_same<any,__uint128_t>::value,fastIO>::type&operator<<(any t){if(!t){put(48);return*this;}int len=0;while(t)sta[len++]=char(t%10+48),t/=10;while(len--)put(sta[len]);return*this;}template<typename any1,typename any2>fastIO&operator<<(const std::pair<any1,any2>&t){return*this<<t.first<<' '<<t.second;}template<typename any>fastIO&write(const any&t){return*this<<t;}template<typename any,typename...args>fastIO&write(const any&t1,const args&...t2){return(*this<<t1).write(t2...);}~fastIO(){fwrite(obuf,p3-obuf,1,stdout);}}fio;
using loli=long long;
using venti=__int128_t;
using pii=std::pair<int,int>;
constexpr int kN=1001;
int p[kN][kN],n,m,cnt,f[kN*kN];
struct edge{int u,v,w;bool operator<(const edge&_t)const{return w<_t.w;}}e[4*kN*kN];
inline int find(int x){return f[x]==x?x:f[x]=find(f[x]);}
signed main(){
//	freopen(".in","r",stdin);
//	freopen(".out","w",stdout);
	fio>>n>>m;
	for(int i=1;i<=n;i++)for(int j=1;j<=m;j++)fio>>p[i][j];
	auto d=[&](int x,int y){return (x-1)*m+y;};
	for(int i=d(n,m);i--;)f[i]=i;
	for(int i=1;i<=n;i++)for(int j=1;j<=m;j++){
		if(i>1)e[++cnt]={d(i,j),d(i-1,j),std::max(p[i][j],p[i-1][j])};
		if(j>1)e[++cnt]={d(i,j),d(i,j-1),std::max(p[i][j],p[i][j-1])};
		if(i<n)e[++cnt]={d(i,j),d(i+1,j),std::max(p[i][j],p[i+1][j])};
		if(j<n)e[++cnt]={d(i,j),d(i,j+1),std::max(p[i][j],p[i][j+1])};
	}
	std::sort(e+1,e+1+cnt);
	int x=d(1,1),y=d(n,m);
	for(auto[u,v,w]:e){
		int fx=find(u),fy=find(v);
		if(fx==fy)continue;else f[fx]=fy;
		if(find(x)==find(y))return std::cerr<<clock()<<'\n',fio<<w,0;
	}
	return 0;
}