#include <fstream>
#include <iostream>
#include <vector>

int main() {

	//std::ifstream inf("Text.txt");	std::cin.rdbuf(inf.rdbuf());

	int N;
	std::cin >> N;

	std::vector<bool> flg(N + 1, true);
	for (int i = 2; i*i <= N; i++) {
		if (flg[i]) {
			for (int j = i + i; j <= N; j += i) {
				flg[j] = false;
			}
		}
	}

	int ans = 0;
	for (int i = 2; i <= N; i++) {
		ans += i * flg[i];
	}

	std::cout << ans << std::endl;

	return 0;
}