include <iostream>

define ll long long

using namespace std; int main() { ll l,r; cin >> l >> r; ll sum = (l+r) * (r-l+1) / 2; while (l%13 != 0) l++; while (r%13 != 0) r--; ll s13 = (l+r) * ((r-l) / 13 + 1) / 2; cout << sum - s13; }