#include <bits/stdc++.h>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");


int main()
{
  long long unsigned n, i, j, c; c = 0;
  vector <bool>A(n + 3, 1);
  fin >> n;
  for(i = 2; i*i <= n; ++i)
  {
    if(A[i] == 1)
    {
      for(j = 2; j <= n/i; ++j)
        A[i * j] = 0;
    }
  }
  for(i = 2; i <= n; ++i)
    if(A[i] == 1)
      ++c;
  fout << c;

  return 0;
}