#include <iostream>
using namespace std;

int main(void)
{
	bool prime[1000000];
	unsigned long n;

	for(unsigned long j = 2; j <= 999999; j++)
		prime[j] = true;
	for(int i = 2; i <= 1000; i++) {
		if(prime[i] == true) {
			for(unsigned long j = i * i; j <= 999999; j += i) {
				prime[j] = false;
			}
		}
	}

	while(cin >> n) {
		unsigned cnt = 0;
		for(unsigned long j = 2; j <= n; j++) {
			if(prime[j] == true) {
				cnt++;
			}
		}

		cout << cnt << endl;
	}
	return 0;
}