sucessor = lambda x: x+1
antecessor = lambda x: x-1
 
def sum(x, y):
    if not y:
        return x
    return sum(sucessor(x), antecessor(y))
 
print(sum(3, 5))  # 8
				c3VjZXNzb3IgPSBsYW1iZGEgeDogeCsxCmFudGVjZXNzb3IgPSBsYW1iZGEgeDogeC0xCgpkZWYgc3VtKHgsIHkpOgogICAgaWYgbm90IHk6CiAgICAgICAgcmV0dXJuIHgKICAgIHJldHVybiBzdW0oc3VjZXNzb3IoeCksIGFudGVjZXNzb3IoeSkpCiAgICAKcHJpbnQoc3VtKDMsIDUpKSAgIyA4