take 2 integers; x and y
case 1; if x < y
max(x,y) = y
min(x,y) = x
max(x,y) +min(x,y) = y + x
case 2; if x > y
max(x,y) = x
min(x,y) = y
max(x,y) +min(x,y) = x + y; which equals y + x
case 2; if x = y
max(y,y) = y
min(x,x) = x
max(x,y) +min(x,y) = y + x