疑似线性筛

#include<bits/stdc++.h>
using namespace std;
int v[1000005],prime[1000005];
void primes(int n){
	int flag=0;
	memset(v,0,sizeof(v));
	for(int i=2;i<=n;i++){
		if(v[i]==0){
			v[i]=i;
			prime[++flag]=i;
		}
		for(int j=1;j<=flag;j++){
			if(prime[j]>v[i]||prime[j]>n/i) break;
			v[i*prime[j]]=prime[j];
		}
	}
}
int main(){
	int n;
	cin>>n;
	primes(1000005);
	cout<< prime[n];
}