#danglam228

#include <bits/stdc++.h>
#define ll long long 
using namespace std;
ll l,r;
int main() {
    cin >> l >> r;
    if (l % 2 == 0) {
        l++; 
    }
    if (r % 2 == 0) {
        r--; 
    }
    if (l > r) {
        cout << 0 << endl;
    }
    ll count = (r - l) / 2 + 1;
    ll d = count * (l + r) / 2;
    cout << d << endl;

    return 0;
}