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: Wrong Answer)

a = gets.to_i
b = gets.to_i
c = gets.to_i
x = gets.to_i

x = x / 50
i = 0
sum = 0

y = Array.new

while 10 * (i + 1) <= x 
  i = i + 1
end

if a < i then
  i = a
end

for j in 0..i do
  x = x - 10 * j
  if x % 2 == 1 then
    if c < x && b < (x - 1) / 2 then
      y[j] = -(x - c) / 2 + b + 1
    elsif c < x then
      y[j] = (c + 1) / 2
    elsif b < (x - 1) /2 then
      y[j] = b + 1
    else
      y[j] = (x + 1)/2
    end
  else
    if c < x && b < x / 2 then
      y[j] = -(x - c) / 2 + b + 1
    elsif c < x then
      y[j] = c / 2 + 1
    elsif b < x / 2 then
      y[j] = b + 1
    else
      y[j] = x/2 + 1
    end
  end
  sum = sum + y[j]
  x = x + 10 * j
end

puts sum