#include <iostream>
#include <fstream>

#define F_NAME "ciur"

using namespace std;
const int N = 2e6;
bool ciur[N+5];


ifstream fin ( "ciur.in" );
ofstream fout ( "ciur.out" );

int main()
{
   int n, res;
   fin >> n;

   ciur[0] = ciur[1] = 1, res = 0;
   for ( int i = 2; i * i <= n; i ++ )
      if ( ciur[i] == 0 )
        for ( int j = i * i; j <= n; j += i )
           ciur[j] = 1;
   for ( int i = 2; i <= n; i ++ )
      if ( ciur[i] == 0 )
        res ++;
   fout << res;
    return 0;
}