#include <iostream>
#include <fstream>
using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");
char eratosthenes[2000001];

void prime(int n) {
    int cnt = 0;
    for (int i = 2; i <= n; ++i) {
        if (eratosthenes[i] == '0') {
            ++cnt;
            for (int j = i; j <= n / i; ++j) {
                eratosthenes[i*j] = '1';
            }
        }
    }
    fout << cnt;
}

int main() {
    int n;
    fin >> n;
    for (int i = 2; i <= n; ++i) {
        eratosthenes[i] = '0';
    }
    prime(n);
    return 0;
}