#include <bits/stdc++.h>
using namespace std;
string __fname = "ciur"; ifstream in (__fname + ".in"); ofstream out (__fname + ".out"); 
#define cin in 
#define cout out

int main(){
    int n;
    cin >> n;
    vector <bool> a (n + 2);
    for (int i = 2; i < n; i++){
        if (a[i] == false){
            for (int j = i + i; j < n; j += i){
                a[j] = true;
            }
        }
    }
    int k = 0;
    for (int i = 2; i < n; i++){
        if (a[i] == false) k++;
    }
    cout << k;
    return 0;
}