#include<iostream>
#include<cmath>
#include<vector>
using namespace std;

int main() {
	int n, cnt; 
	while (cin >> n) {
		cnt = 0;
		vector<bool> v(n + 1, true);
		for (int i = 2; i*i <= n; i++) {
			if (v[i]) {
				for (int j = 2 * i; j <= n; j += i) {
					v[j] = false;
				}
			}
		}
			for (int i = 2; i <= n; i++) {
				if (v[i]) cnt++;
			}
		cout << cnt << endl;
	}
	return 0;
}