#include <bits/stdc++.h>
using namespace std;

ifstream fin("ciur.in");
ofstream gout("ciur.out");

int main(){
    int n;
    fin >> n;
    bool prim[n+1];

    for (int i = 0; i <= n; i++){
        prim[i] = true;
    }

    prim[0] = prim[1] = false;

    for (int p = 2; p * p <= n; p++){
        if (prim[p]) {
            for (int m = p * p; m <= n; m += p){
                 prim[m] = false;
            }
        }
    }
                          
    int cnt = 0;
    for (int i = 0; i <= n; i++){
        if (prim[i])
           cnt++;
    }

    gout << cnt;

return 0;
}