#include <bits/stdc++.h>
using namespace std;
const int maxn = 2e6 + 9;
bool ciur [maxn];
	
int main(){
	freopen ("ciur.in" , "r", stdin);
	freopen("ciur.out" , "w", stdout);
	int n;
	cin >>n;
	ciur[0] = ciur[1] = true;
	int rs = 0;
	for(int i = 2; i <= n; i++){
		if(ciur[i] == false){
			rs++;
			for(int j = i * 2; j <= n; j+=i){
				ciur[j] = true;
			}
		}
	}
	cout << rs;
	return 0;
}