Problem:
Score : 200 points

Problem Statement

We have A cards, each of which has an integer 1 written on it. Similarly, we also have B cards with 0s and C cards with -1s.

We will pick up K among these cards. What is the maximum possible sum of the numbers written on the cards chosen?

Constraints

All values in input are integers.

0 \leq A, B, C

1 \leq K \leq A + B + C \leq 2 \times 10^9

Input

Input is given from Standard Input in the following format:

A B C K

Output

Print the maximum possible sum of the numbers written on the cards chosen.

Sample Input 1

2 1 1 3

Sample Output 1

2

Consider picking up two cards with 1s and one card with a 0.
In this case, the sum of the numbers written on the cards is 2, which is the maximum possible value.

Sample Input 2

1 2 3 4

Sample Output 2

0

Sample Input 3

2000000000 0 0 2000000000

Sample Output 3

2000000000

Solution in C++ (GCC 9.2.1) (judge verdict: Accepted)

#include <bits/stdc++.h>
using namespace std;
using ll = long long;

#define REP(i, n) for(int (i) = 0; (i) < (n); ++(i))
#define REPR(i, n) for(int (i) = (n); (i) >= 0; --(i))
#define FOR(i, n, m) for(int (i) = (n); (i) < (m); ++(i))

constexpr int INF = 1e9;
//constexpr ll INF = 1LL<<61;
constexpr ll mod = 1e9+7;


int main(){
  ll A, B, C, K;
  cin >> A >> B >> C >> K;
  ll sum = 0;
  sum += min(K, A);
  K -= A;
  K -= B;
  if(K > 0){
    sum -= K;
  }
  cout << sum << endl;
  return 0;
}