时间有点离谱......

#include <bits/stdc++.h>
using namespace std;
const int M=20000000;
vector<bool> is(M+1,1);
vector<int> p;
void sieve(){
    is[0]=is[1]=0;
    for(int i=2;i<=M;i++){
        if(is[i]){
            p.push_back(i);
            if((long long)i*i<=M){
                for(int j=i*i;j<=M;j+=i) {
                    is[j]=0;
                }
            }
        }
    }
}
signed main(){
    ios::sync_with_stdio(0);cin.tie(0);
    sieve();
    int n;
    if(cin>>n) {
        if(n>0&&n<=p.size()) {
            cout<<p[n-1]<<endl;
        }
		else{
            cerr<<"Range exceeded, increase MAX_LIMIT"<<endl;
        }
    }
    return 0;
}