#include <iostream>
using namespace std;

int main() {
    int a, b;
    cin >> a >> b;

    int zbir = 0;
    for(int i = a; i <= b; i++) {
        if(i % 2 == 1) {
            zbir += i;
        }
    }
    cout << zbir << endl;
    return 0;
}