#include <iostream>
#include <fstream>

std::ifstream f("ciur.in");
std::ofstream g("ciur.out");

int N, i, j;
bool prime[2000001];
size_t cnt;

int main()
{
    f >> N;

    for(i = 2; i <= N; ++i)
        prime[i] = true;

    for(i = 2; i <= N; ++i)
        if(prime[i]) {
            ++cnt;
            for(j = i + i; j <= N; j = j + i)
                prime[j] = false;
        }

    g << cnt << '\n';

    return 0;
}