Problem:
Score : 100 points

Problem Statement

You are given positive integers A and B.

If A is a divisor of B, print A + B; otherwise, print B - A.

Constraints

All values in input are integers.

1 \leq A \leq B \leq 20

Input

Input is given from Standard Input in the following format:

A B

Output

If A is a divisor of B, print A + B; otherwise, print B - A.

Sample Input 1

4 12

Sample Output 1

16

As 4 is a divisor of 12, 4 + 12 = 16 should be printed.

Sample Input 2

8 20

Sample Output 2

12

Sample Input 3

1 1

Sample Output 3

2

1 is a divisor of 1.

Solution in C# (Mono 4.6.2.0) (judge verdict: Runtime Error)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace _20190308_07 {
    class Program {
        static void Main(string[] args) {
            var n = int.Parse(Console.ReadLine());
            var line = Console.ReadLine().Split(' ').Select(x => long.Parse(x)).ToArray();
            var a = GCD(line[0], line[1]);
            for (int i = 2; i < n; i++) {
                a = GCD(a, line[i]);
            }
            Console.WriteLine(a);
        }

        static long GCD(long a, long b) {
            if (a < b)
                GCD(b, a);
            while (b != 0) {
                var remainder = a % b;
                a = b;
                b = remainder;
            }
            return a;
        }

    }
}