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 C++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <iostream>
 
int main(void){
  
  int N;
  std::cin >> N;
  int field[2][N];
  
  int cnt = N;
  int elm = 0;
  	while (--cnt){
    	std::cin >> field[elm][cnt];
      	elm += 1;
    }
  
  int sum = 0;
  int max = 0;
  for(int i = 0; i < N; i++){
 	 for(int j = 0; j < N; j++){
   	 	if(i >= j)
          sum += field[0][j];
        else
          sum += field[1][j] = field[0][j - 1];
     }
     if(sum > max){
       max = sum;
     }
  }
  
  std::cout << max << std::endl;
  
  return 0;
}