#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);
    vector<int>prime;

    for (int i = 2; i <= n; i++) {
        if (prim[i] == true)
            prime.push_back(i);

        for (int j = i*2; j <= n; j += i)
            prim[j] = false;
    }

    fout<<prime.size()<<'\n';
    return 0;
}