#include <iostream>

using namespace std;

int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    int x = 0, p[100] = {}, i, j, n;
    f >> n;
    for(i = 2; i <= n; i++)
        p[i] = 1;
    for(i = 2; i <= n; i++)
        if(p[i])
        {
            x++;
            for(j = i+i; j <= n; j += i)
                p[j] = 0;
        }
    g << x;
    return 0;
}