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

ifstream f("ciur.in");
ofstream g("ciur.out");

void ciur(vector<bool> &v, int n) {
    v[0] = v[1] = false;
    for(int i = 2; i * i <= n; i++) {
        if(v[i]) {
            for(int j = i * i; j <= n; j += i)
                v[j] = false;
        }
    }
}

int main() {
    int n, ans = 0;
    f >> n;
    vector<bool> v(n + 1, true);
    ciur(v, n);
    for(bool x : v) if(x == true) ans++;
    g << ans;
    return 0;
}