#include <iostream>
using namespace std;

int main() {
	int a, b, ans0 = 0, ans1 = 0, n;
	cin >> a >> b;
	if (a % 2 == 0 && b % 2 == 1) {
		n = (b - a + 1) / 2;
		ans0 = (a + n - 1)*n;
		ans1 = (a + n)*n;
	}
	else if (a % 2 == 0 && b % 2 == 0) {
		n = (b - a + 1) / 2;
		ans0 = (a + n)*(n + 1);
		ans1 = (a + n)*n;
	}
	else if (a % 2 == 1 && b % 2 == 0) {
		n = (b - a + 1) / 2;
		ans1 = (a + n - 1)*n;
		ans0 = (a + n)*n;
	}
	else if (a % 2 == 1 && b % 2 == 1) {
		n = (b - a + 1) / 2;
		ans1 = (a + n)*(n + 1);
		ans0 = (a + n)*n;
	}
	cout << ans0 - ans1 << endl;
		return 0;
}