#include <bits/stdc++.h>

using namespace std;

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

const int DIM = 2e6 + 7;

bool viz[DIM];

int main()
{

   int n;
   in >> n;

   int cnt = 0;


   if(n >= 2)
   cnt++;

   for(int i = 3; i <= n; i += 2)
    if(viz[i] == false)
    {
        cnt++;
        for(int j = 2 * i; j <= n; j +=i)
            viz[j] = true;
    }

    out << cnt;

    return 0;
}