CODE

#include <iostream>

using namespace std;
int l, r;

int main(void) {
  scanf("%d %d", &l, &r);
  if (l > r) l ^= r, r ^= l, l ^= r;
  int ans = 0;
  for (int i = l + 1; i < r; ++i) if (i & 1) ans += i;
  return printf("%d\n", ans), 0;
}