#include <bits/stdc++.h>
using namespace std;
bool Prim[2000013];
int sol(0),n,sf(0);
int main()
{
 ifstream cin("ciur.in");
 ofstream cout("ciur.out");
 cin>>n;
 for (int i=2;i<=n;++i)
   if (Prim[i]==0) 
    {
	++sol;
    for (int j=2; i*j<=n; ++j) Prim[i*j]=1;
    }
 cout<<sol;
 return 0;
}