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

#define NMAX 2000002

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

bitset<NMAX> marked;

int ciur(const int N) {

    if (N <= 1)
        return 0;

    int primes = 1;

    for (int i = 3; i <= N; i += 2) {
        if (!marked[i]) {
            primes++;

            for (int j = 1LL * i * i; j <= N; j += i)
                marked[j] = 1;
        }
    }

    return primes;
}

int main() {

    int N;

    fin >> N;

    fout << ciur(N);

    return 0;
}