#include<iostream>
#include<vector>
#include<string>
#define T 1000000
using namespace std;

signed main() {
	vector<bool>hantei(T, true);
	vector<int>sosuu(T);
	int s = 0;
	for (int a = 2; a < T; a++) {
		if (hantei[a]) {
			s++;
			for (int b = a * 2; b < T; b+=a)hantei[b] = false;
		}
		sosuu[a]=s;
	}
	while (cin >> s)cout << sosuu[s] << endl;
}