#include <fstream>

using namespace std;

const int MAX_N = 2000000;

bool V[1 + MAX_N];

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

int main() {
    int n, i, j, ans = 0;

    in >> n;

    for(i = 2; i <= n; i++) {
        for(j = i*i; j <= n; j += i) {
            V[j] = 1;
        }
    }
    for(i = 2; i <= n; i++) {
        ans += (1 - V[i]);
    }

    out << ans << '\n';
    return 0;
}