#include<iostream>
using namespace std;

int get_num_of_under_n(int n) {
	bool* numbers = new bool[n + 1];
	for (int i = 2; i < n + 1; i++) {
		numbers[i] = true;
	}
	for (int i = 2; i < sqrt(n); i++) {
		if (numbers[i] == true) {
			for (int j = 0; i*(j + 2) <= n; j++) {
				numbers[i*(j + 2)] = false;
			}
		}
	}
	int ans = 0;
	for (int i = 2; i < n + 1; i++) {
		if (numbers[i] == true)ans++;
	}
	return ans;
}
int main() {
	int n;
	while (cin>>n) {
		cout << get_num_of_under_n(n)<<endl;
	}
}