质数 埃氏

#include<bits/stdc++.h>
using namespace std;
define N 1000000
int b[1000005], n, cnt;
int main(){
	scanf("%d",&n);
	for(int i = 2; i*i <= N; i++){
		for(int j = i*i; j <= N; j += i)
			b[j] = 1;
	}
	for(int i = 2; i <= N; i++)
		if(b[i] == 0){
			cnt++;
			if(cnt == n) cout<<i<<endl;
		}
			
	return 0; 
}