Write a function named `pairs(a,b,c,d)` that takes four integers as its input and checks whether the sum of any two of t

[answerhappygod]

Write a function named `pairs(a,b,c,d)` that takes four
integers as its input and checks whether the sum of any
two of these integers is equal to the sum of the other two.
If so, the function RETURNs this sum. Otherwise, it RETURNs -1.
For example, `pairs(1,2,3,4)` should return 5,
because 1 + 4 = 2 + 3 = 5.
Another example, `pairs(11,22,13,20)` should return 33,
because 11 + 22 = 13 + 20 = 33.
Another example, `pairs(1,2,3,5)` should return -1,
because no such two pairs exist among these numbers.
"""
def pairs(a,b,c,d):
# remove the following line to solve this question
return