#include<bits/stdc++.h>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int n, i, k, cnt;
char a[2000005];
int main()
{
	fin >> n;
	for (i = 2; i <= n; i++) a[i] = 0;
	for (i = 2; i <= n ; i++)
	if (a[i] == 0) {
	cnt ++;
	k = 2;
	while( i*k <= n )
   {
       a[i*k] = 1;
       k++;
   }
   }
	k = 0;
	fout << cnt;
	return 0;
}