#include <iostream>
#include <fstream>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

bool fr[2000002];

int main()
{
    long long i, j, n, k= 0;

    fin>>n;;
    for (i = 2; i <= n; ++i){
            if (fr[i] == 0){
                fr[i] = 1;
                k++;
                for (j = i*i; j <= n; j+=i){
                    fr[j] = 1;
                }
            }
    }
    /*
    for (i = 2; i <= N; i++)
        if( marked[i] == 2) nr_prime++;
            */
   fout<<k;
    return 0;
}