#include<iostream>
#include<cmath>
using namespace std;
typedef long long ll;
ll prime[1000001];
ll length = 0;
void insert(ll p) { prime[length] = p; length++; return; }
int main(){
	insert(2);
	for (ll i = 3; i < 1000000; i += 2) {
		for (ll j = 0; j < length; j++)
			if (i%prime[j] == 0)goto cont;
			else if (prime[j] > sqrt(i))break;
		insert(i);
	cont:;
	}
	ll n; while (cin >> n) {
		ll ans = 0;
		while (prime[ans] <= n&&ans < length) {
			ans++;
		}
		cout << ans << endl;
	}
	return 0;
}