#include <iostream>
#include <cstdio>
#include <algorithm>
using namespace std;

const int MAXN = 1e6;

bool is_prime[MAXN];
int prime_count[MAXN];

void init() {
	fill(is_prime, is_prime + MAXN, true);
	int cnt = 0;
	for (int i = 2; i < MAXN; ++i) {
		if (is_prime[i]) {
			++cnt;
			for (int j = i + i; j < MAXN; j += i) {
				is_prime[j] = false;
			}
		}
		prime_count[i] = cnt;
	}
}

int main() {
	//freopen("0009.txt", "r", stdin);
	init();
	int n;
	while (cin >> n) {
		cout << prime_count[n] << "\n";
	}
}