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 (GCC 5.4.1) (judge verdict: Accepted)

#include<stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
 

 
int main()
{
    int X,A,B;
  int i=0;      
 // 整数の入力
    scanf("%d", &X);
    scanf("%d", &A);
    scanf("%d", &B);
/*
  // printf("%d\n",N);
    for(i = 1; i < N +1;i++){
      scanf("%d %d %d", &t[i],&x[i], &y[i]);      
//      printf("%d %d %d", t[i],x[i], y[i]);
      t_temp=t[i] - t[i-1];
/*      if(0 < x[i] - x[i-1]) x_temp=x[i] - x[i-1];
      else  x_temp=x[i-1] - x[i];
      if(0 < y[i] - y[i-1]) y_temp=y[i] - y[i-1];
      else  y_temp=y[i-1] - y[i];
 */
  /*
      x_temp=abs(x[i] - x[i-1]);
      y_temp=abs(y[i] - y[i-1]);
      
//      printf("%d %d %d\n", t_temp,x_temp, y_temp);
 //     printf("%d \n", abs((t_temp-(x_temp+y_temp))));
  //    printf("%d \n", t_temp-(x_temp+y_temp));
      if((0>(t_temp-(x_temp+y_temp))) || ((1==(t_temp-(x_temp+y_temp)) %2))){
//      if(0>(t_temp-(x_temp+y_temp))){
//        if(0 != abs((t_temp-(x_temp+y_temp)) ) %2 ){
        printf("No\n");
        return 0;
      }
    }
 */

  while(1){

    if(0>X-A-(B*i)) break;
  i++;
  }
  
  printf("%d\n",X-A-(B*(i-1)));

return 0;
}