#include <iostream>
#include <math.h>
#include <fstream>

using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");

int main()
{
    int n, r = 0, v[100];
    f >> n;

    for(int i = 2; i < 100; i++)
        v[i] = 1;

    for(int i = 2; i <= n; i++){
        if(v[i] == 1)
            for(int d = i*i; d <= n; d += i)
                v[d] = 0;
    }

    for(int i = 0; i < n; i++)
        r += v[i];

    g << r;

    return 0;
}