011. Ski Sum
time limit per test
1 second
memory limit per test
256 megabytes
input
standard input
output
standard output

Your favorite ski resort has a certain number of easy trails, more difficult trails, most difficult trails, and expert-only trails. Given these values, find how many trails there are at the ski resort. Note that the same trail will never be two different difficulties.

Input

The only line of input contains 4 space-separated integers, each representing the number of easy trails, more difficult trails, most difficult trails, and expert-only trails, respectively.

Output

Print one positive integer: the total number of ski trails at the mountain.

Example
Input
20 16 13 6
Output
55