#include <bits/stdc++.h>
#define Max 100001
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");

bool a[2000001];
int n,s;

int main()
{
  f>>n;

  for(int i=2;i*i<=n;++i)
    if(!a[i])
  {
      int j=2;
      while(i*j<=n)
      {
          a[i*j]=1;
          j++;
      }
  }

  for(int i=2;i<=n;++i)
    if(!a[i])
       s++;

  g<<s;



}