#include <bits/stdc++.h>

using namespace std;

#define nmax 2000000

bool prim[nmax];

void sieve() {
    prim[1] = true;
    for (int i = 3; i * i<= nmax; i += 2) {
        if (!prim[i]) {
            for (int j = i * i; j <= nmax; j += i) {
                prim[j] = true;
            }
        }
    }
    for (int i = 4; i <= nmax; i += 2) {
        prim[i] = true;
    }
}

int main() {
    ifstream in("ciur.in");
    ofstream out("ciur.out");

    int n;

    in >> n;
    sieve();
    int nrprim = 1;
    for (int i = 3; i <= n; ++i) {
        if (!prim[i]) ++nrprim;
    }
    out<<nrprim;
}