#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>
using namespace std;

int main() {
    ifstream cin("ciur.in");
    ofstream cout("ciur.in");
    int n;
    cin>>n;
    vector<bool> prim(n+1);
    fill(prim.begin(), prim.end(), true);
    for (int i = 2; i <= n; i++) {
        if (prim[i]) {
            for (int j = 2*i; j <=n; j+=i) {
                prim[j] = false;
            }
        }
    }
    cout<<count(prim.begin()+2, prim.end(), true);
    return 0;
}