Problem:
Score : 100 points

Problem Statement

You went shopping to buy cakes and donuts with X yen (the currency of Japan).

First, you bought one cake for A yen at a cake shop.
Then, you bought as many donuts as possible for B yen each, at a donut shop.

How much do you have left after shopping?

Constraints

1 \leq A, B \leq 1 000

A + B \leq X \leq 10 000

X, A and B are integers.

Input

Input is given from Standard Input in the following format:

X
A
B

Output

Print the amount you have left after shopping.

Sample Input 1

1234
150
100

Sample Output 1

84

You have 1234 - 150 = 1084 yen left after buying a cake.
With this amount, you can buy 10 donuts, after which you have 84 yen left.

Sample Input 2

1000
108
108

Sample Output 2

28

Sample Input 3

579
123
456

Sample Output 3

0

Sample Input 4

7477
549
593

Sample Output 4

405

Solution in Ruby (2.3.3) (judge verdict: Runtime Error)

n = gets.to_i
xs = [gets.split.map(&:to_i), gets.split.map(&:to_i)]
memo = [[0] * n, [0] * n]
2.times do |i|
  n.times do |j|
    memo[i][j] =
    if i == 0
      if j == 0
        xs[0][0]
      else
        memo[i][j-1] + xs[i][j]
      end
    else
      if j == 0
        memo[i-1][j] + xs[i][j]
      else
        [memo[i][j-1], memo[i-1][j]].max + xs[i][j]
      end
    end
  end
end
p memo[1][n-1]