#include <iostream>
#include <fstream>
using namespace std;
int main()
{
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    int N;
    int i, nc=0;
    fin>>N;
    bool A[N+5];
    for(i=2; i<=N; ++i)
        A[i]=false;
    for(i=2;i<N;++i)
    {
        if(A[i] == false)
        {
            ++nc;
            int p=2;
            while(i*p<=N)
            {
                A[i*p] = true;
                ++p;
            }
        }
    }
    fout<<nc;
    return 0;
}