#include <fstream>
#include <iostream>

const int NMAX = 20001;
bool Sir[NMAX];

int main()
{
    int N;
    std::ifstream f("ciur.in");
    f >> N;
    f.close();

    int i = 2, Prime = N - 1;
    do
    {
        if(!Sir[i])
            for(int j = i * i; j <= N; j += i)
                if(!Sir[j])
                {
                    Prime--;
                    Sir[j] = true;
                }
        i++;
    } while(i * i <= N);

    std::ofstream g("ciur.out");
    g << Prime;
    return 0;
}