#include <bits/stdc++.h>
#define PI 3.14159265359
using namespace std;
const int64_t mod = 1e9 + 7;

int main() {
	int N;
	cin >> N;

	vector<int> v(N);
	for (int i = 0; i < N; i++) {
		v.at(i) = i + 1;
	}

	for (int i = 0; i < N; i++) {
		int& n = v.at(i);
		if (n < 2) {
			n = 0;
		}
		else {
			for (int j = i + 1; j < N; j++) {
				int& m = v.at(j);
				if (m % n == 0) {
					m = 0;
				}
			}
		}

		if (i == N - 1) break;
	}

	int sum = 0;
	for (int i = 0; i < N; i++) {
		sum += v.at(i);
	}

	cout << sum << endl;
}