#include <bits/stdc++.h>
using namespace std;

bool prime(int n) {
	if (n < 2) return false;
	for (int i = 2; i < sqrt(n) + 1; i++) {
		if (n % i == 0) return false;
	}
	return true;
}

int main() {
	vector<int> v = vector<int>(1, 0);
	for (int i = 1; i < 1000000; i++) {
		if (prime(i)) {
			v.push_back(v.back() + 1);
		} else {
			v.push_back(v.back());
		}
	}
	int n;
	while (cin >> n) {
		if (n == 1) {
			cout << 0 << endl;
		} else {
			cout << v[n] + 1 << endl;	
		}
	}
}