#include <bits/stdc++.h>

using namespace std;

int main()
{
    ifstream fin{"ciur.in"};
    ofstream fout{"ciur.out"};

    int N; fin >> N;

    vector<bool> prim(N + 1, true);

    for(int i = 2; i * i <= N; ++i)
        if(prim[i] == true)
            for(int j = i * i; j <= N; j += i)
                prim[j] = false;

    fout << count(prim.begin(), prim.end(), true) - 2;
}