#include <bits/stdc++.h>
using namespace std;

int main() {
	int n, m;
	long long ans = 0;
	cin >> n >> m;
	if(n % 2 == 0) n += 1;
	for(int i = n; i <= m; i += 2) {
		ans += i;
	}
	cout << ans;
	return 0;
}