#include <bits/stdc++.h>
using namespace std;
ifstream fin("ciur.in");
ofstream  fout("ciur.out");
bool v[2000000];
int main()
{
  long long unsigned n, cnt = 0;
  fin >> n;
  if(n == 2)
    fout << 1;
  for(int i = 4 ; i <= n; i=i+2)
    {
      if(v[i] % 2 == 0)
        v[i] = true;
    }
  for(int i = 3; i <= n; i=i + 2)
    {
      if(v[i] == false)
        for(int j = i * i; j <= n; j = j + 2 * i)
            v[i] = true;
    }
    for(int i = 2; i <= n; i++)
    {
        if(v[i] == false)
            cnt++;
    }
    fout << cnt;



}