import std.stdio;

void main() {
	long n;
	readf("%s", &n);

	auto a = new uint[n + 1];
	a[1..$] = 1;
	foreach (i;2..n + 1) {
		for (auto j = i;j <= n;j += i) {
			++a[j];
		}
	}

	long s;
	foreach (long i;1..n + 1) {
		s += i * a[i];
	}

	writeln(s);
}
