#include<bits/stdc++.h>
#define ll long long
using namespace std;
const int N=1.1e7+10;
int n,p[N<<1];
char s[N<<1];
inline void read(){
	char c=getchar();
	while(c<'a'||c>'z')c=getchar();
	s[++n]='#';
	while(c>='a'&&c<='z'){
		s[++n]=c;
		s[++n]='#';
		c=getchar();
	}
}
int main(){
	read();
	for(int i=2,maxr=1,mid=1;i<=n;i++){
		if(mid<i&&i<maxr)p[i]=min(p[mid*2-i],maxr-i+1);
		while(s[i-p[i]-1]==s[i+p[i]+1]&&i-p[i]-1>0&&i+p[i]+1<=n)p[i]++;
		if(i+p[i]>maxr)maxr=i+p[i],mid=i;
	}
	int ans=0;
	for(int i=1;i<=n;i++)ans=max(ans,p[i]);
//	for(int i=1;i<=n;i++)printf("%d ",p[i]);
	printf("%d",ans);
	return 0;
}

WA on test 2,3,4,9,10,11

实现细节可能比较奇怪。