Pairs#3655
Given two ranges of integers and , determine the number of pairs that satisfy the following conditions:
x \neq y, a \leq x \leq b, c \leq y \leq d.
A single line contains four integers , , , (a \leq b, c \leq d, -10^8 \leq a, b, c, d \leq 10^8).
Output a single line containing the number of valid pairs.
Example 1