#include <iostream>
using namespace std;
const int SIZE = 100;
int main(void)
{
int p[SIZE];
int n, tot, i, cn;
tot = 0;
cin >> n;
for (i = 1; i <= n; i++)
p[i] = 1;
for (i = 2; i <= n; i++){
if (p[i] == 1)
tot++;
cn = i * 2;
while (cn <= n) {
p[cn] = 0;
cn += i;
}
}
cout << tot << endl;
return 0;
}
输入:30输出:1
