#include <bits/stdc++.h>

int ri() {
	int n;
	scanf("%d", &n);
	return n;
}

int main() {
	int a = ri();
	int b = ri();
	int s = ri();
	int64_t res = 0;
	for (int i = 1; i <= a; i++) {
		int max = std::min(b, s / i);
		res += ((int64_t) (b + 1) * max - (int64_t) max * (max + 1) / 2) * (a - i + 1);
	}
	std::cout << res << std::endl;
	return 0;
}