Consider integer numbers from 0 to n - 1 written down along the circle in such a way that the distance between any two neighboring numbers is equal (note that 0 and n - 1 are neighboring, too).

Given n and firstNumber, find the number which is written in the radially opposite position to firstNumber.

Example

For n = 10 and firstNumber = 2, the output should be

solution(n, firstNumber) = 7.

Input/Output

• [execution time limit] 3 seconds (java)

• [memory limit] 1 GB

• [input] integer n

  A positive even integer.

  Guaranteed constraints:

  4 ≤ n ≤ 20.

• [input] integer firstNumber

  Guaranteed constraints:

  0 ≤ firstNumber ≤ n - 1.

• [output] integer

풀이

int solution(int n, int firstNumber) {
    int half = n / 2;
    int result = firstNumber + half;
    
    if (result > n - 1) return result % n;
    
    return result;
}