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)

lines = readlines.join.split.map(&:to_i)
range = lines.shift
ary = []
2.times do 
    ary << lines.slice!(0..range-1)
end
ans = []
for i in 0..range do
    ans << (ary[0].slice(0..i)).append(ary[1].slice(i..range-1))
end
ans.map!{|t| t.flatten}
ans.map!{|f| f.sum }
p ans.max