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

using namespace std;

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

int n, r;
bool v[2000005];

int main()
{

    f >> n;

    for(int i = 2; i <= n; i++){
        if(v[i] == false){
            for(int d = i*i; d <= n; d += i)
                v[d] = true;
            r++;
        }

    }

    g << r;

    return 0;
}