# include <bits/stdc++.h>
using namespace std;

int n, p;
bool a[2000005];
int main(){
	ifstream cin("ciur.in");
	ofstream cout("ciur.out");

	cin>>n;
	p=0;
	for (int i = 2; i<=sqrt(n); i++){
	
  		if (!a[i]){
  			p++;
    		for (int j = i* i; j<=n; j+=i ){
      			a[j]= true;
      			}
      
      		}
 		}
 	cout<<p+2;
 	return 0;
}