#include <bits/stdc++.h>

using namespace std;
const long long NR = 2000001;

bool ciur[NR];
int n;
ifstream in ("ciur.in");
ofstream out ("ciur.out");
signed main() {


    for (int i = 2; i <= 2000000; ++i) {
        if (!ciur[i]) {
            for (int j = i + i; j <= 2000000; j += i) {
                ciur[j] = true;
            }
        }
    }

    in >> n;
    int sum = 0;
    for (int i = 2; i <= n; ++i) {
        sum += !ciur[i];
    }
    out << sum << '\n';
    return 0;
}