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: Accepted)

#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
using namespace std;
/////////////////// TYPES & MACROS ///////////////////////////////
#define INFLL 0x3fffffffffffffffLL
#define INF 0x3fffffff
#define mp make_pair
#define eb emplace_back
#define pb push_back
#define all(x) x.begin(),x.end()
#define exist(s,e) (s.find(e)!=s.end())
#define ff first
#define ss second
#define EPS 1e7
typedef long long int ll;
typedef unsigned long long int ull;
typedef long double ld;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
typedef tree<int,null_type,less<int>,rb_tree_tag,
tree_order_statistics_node_update> indexed_set;
const ll MOD=1e9+7;
/////////////////// DEBUG MODE ///////////////////////////////////
#define D(x) cerr<<"DEBUG: "<<#x<<" is: "<<x<<'\n'
#define error(args...) {string _s=#args; replace(all(_s),',',' ');\
stringstream _ss(_s); istream_iterator<string> _it(_ss); err(_it, args);}
void err(istream_iterator<string>) { cout<<endl;}
template<typename T, typename... Args>
void err(istream_iterator<string> it, T a, Args... args) {
	cerr << *it << " = " << a << endl;
	err(++it, args...);
}
/////////////////// GLOBAL VARIABLES /////////////////////////////
vector<vector<int>> adj; vector<bool> vis; vector<int> color;
/////////////////// FUNCTIONS ////////////////////////////////////
template<class T>
T maxx(T a, T b) {return a>b?a:b;}
template<typename T, typename... Args>
T maxx(T a, T b, Args... args){return maxx(a>b?a:b, args...);}
ll mexp(ll x, ll n, ull m){
  ll res=1;  while(n){if(n&1) res=(res*x)%m;n>>=1; x=((x%m)*(x%m))%m;}
  return res;
}
template<class T>
T minn(T a, T b) {return a<b?a:b;}
template<typename T, typename... Args>
T minn(T a, T b, Args... args){return minn(a>b?a:b, args...);}
bool ispow2(ll x){ return x && (!(x&(x-1))); }
ld pow(ld a, int n) {
  if(n == 0) return 1;if(n == 1) return a;
  double t = pow(a, n/2);return t * t * pow(a, n%2);
}

/////////////////// MAIN STARTS //////////////////////////////////
int main(){
  ios::sync_with_stdio(0);  cin.tie(0);   cout<<fixed; cerr<<fixed;
  cout<<setprecision(10); cerr<<setprecision(3);
  #ifdef DEBUG
  freopen("ip.txt","r",stdin); //freopen("op.txt","w",stdout);
  clock_t tStart = clock();
  #endif

	ll x,a,b; cin>>x>>a>>b;
	x-=a;
	cout<<x%b<<'\n';


	#ifdef DEBUG
	cerr<<"\nExecution time: "<<(((double)clock() - tStart)/CLOCKS_PER_SEC)*1000<<"ms.\n";
	#endif
  return 0;
}