#include <bits/stdc++.h>
using namespace std;
     
#define MaxN 2000000
     
char prime[MaxN + 1];
int N;
     
int main() {
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);	    
 
    int i, j, res = 0;
     
    cin >> N;
    for(i = 2; i * i <= N; i++)
   	if(!prime[i]) 
    	for(j = i * i; j <= N; j = j + i) prime[j] = 1;
     
    for(i = 2; i <= N; i++) res = res + (prime[i] == 0);
   	cout << res;
     
     
return 0;
}