#include <iostream>
#include <fstream>
std::ifstream fin ("ciur.in");
std::ofstream fout ("ciur.out");
int main()
{
    int n,c=0;
    fin >> n;
    bool C[n+1];
    std::fill(std::begin(C),std::end(C), 0)
    for (int i=2;i<=n;i++)
    {
        if (C[i]==false) {
            c++;
            for (int j=i;j*i<=n;j++)
            {
                C[j*i]=true;
            }
        }
    }
    fout << c;
    return 0;
}