#include <fstream>
using namespace std;

ifstream cin("ciur.in");
ofstream cout("ciur.out");

int prim(int n){
    if(n < 2){
        return 0;
    }
    if(n % 2 == 0 && n != 2){
        return 0;
    }
    for(int d = 3; d * d <= n; d += 2){
        if(n % d == 0){
            return 0;
        }
    }
    return 1;
}

int main(){
    int n, cnt = 0;
    cin >> n;
    for(int i = 2; i <= n; ++i){
        if(prim(i)){
            cnt++;
        }
    }
    cout << cnt;
    return 0;
}