#include <iostream>
#include <fstream>
#include <math.h>

using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");

int A[2000005];

int main()
{
      int N, i, j, nr = 0;
      f >> N;
      f.close();
      for (i = 2; i <= N; i++)
            if (A[i] == 0)
            {
                  nr++;
                  for (j = i * i; j <= N; j = j + i)
                        A[j] = 1;
            }
      g << nr;
      g.close();
}