#include <iostream>
#include <fstream>
std::ifstream fi("ciur.in");
std::ofstream fo("ciur.out");

bool prime[2000000];

int main()
{
    int n, number = 0;
    fi>>n;
    for(int i = 2; i<=n; ++i)
    {
        if(!prime[i])
        {
            ++number;
            for(int j = 2; i*j<=n; ++j)
            {
                prime[i*j] = 1;
            }
        }
    }
    fo<<number;
}