Oh no! Chalmers Challenge is only one day away and Chalmers Coding Club haven’t had the time
to prepare all tasks. As we all know, competitive programming
problems are created by combining funny problem statements with
computer programming methods. There are $A_{uniq}+A_{reuse}$ problem statement
themes and $B_{uniq}+B_{reuse}$ algorithmic
methods. Some of these are onetrick ponies that only work once
while others are so good they never get old. Out of all the
themes and methods, only $A_{reuse}$ and $B_{reuse}$ are good enough to be
reused continually. How many different problems can be created
by combining all these themes and methods?
Input
Input consists of one line with four spaceseparated
integers: $0 \le A_{uniq},
B_{uniq}, A_{reuse}, B_{reuse} \le 10^9$, the number of
singleuse themes and methods and the number of reusable themes
and methods respectively.
Output
Output a single integer, the number of problems that can be
created in total.
Sample Input 1 
Sample Output 1 
2 3 0 0

2

Sample Input 2 
Sample Output 2 
7 3 0 3

7

Sample Input 3 
Sample Output 3 
82 31 21 44

1037

Sample Input 4 
Sample Output 4 
0 2 1 0

2
