#include <iostream>
#include <math.h>
using namespace std;

int main() {
int a[1001];
int nr = 0, n, i, j;
cout << "Numerele pana la: ";
cin >> n;
for (i = 2; i <= n; i++)
a[i] = 1;
for (i = 2; i <= sqrt(n); i++)
if (a[i] != 0)
for (j = 2; j <= n / i; j++)
a[i*j] = 0;
for (i = 2; i <= n; i++)
if (a[i] != 0)
nr++;
cout << nr << endl;
return 0;
}