#include <bits/stdc++.h>

using namespace std;
const int N = 1000000;
int prime[N];

int main() {
    int idx;
    int flag;
    for (int i = 2; i < N; i++) {
        flag = 1;
        for (int j = 2; j * j < i; j++) //会快很多
//        for (int j = 2; j < sqrt(i); j++)
            if (i % j == 0) flag = 0;
        if (flag == 1) prime[idx++] = i;
    }
    printf("%.2f", (double) clock() / CLOCKS_PER_SEC);
    return 0;
}