#include <bits/stdc++.h>

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