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 i32 = int32_t;
using i64 = int64_t;
using u32 = uint32_t;
using u64 = uint64_t;

using f64 = double;
using f128 = long double;

template <typename T> using Vec = vector<T>;
template <typename K, typename V> using HashMap = unordered_map<K, V>;
template <typename T> using HashSet = unordered_set<T>;

using StrView = string_view;

auto solve(i64 const A, i64 const B, i64 const C, i64 const K) -> void {
  if (K <= A) {
    cout << K << "\n";
    return;
  }

  if (K <= A + B) {
    cout << A << "\n";
    return;
  }

  if (K <= A + B + C) {
    i64 result = A - (K - A - B);
    cout << result << "\n";
    return;
  }

  cout << A - C << "\n";
}

auto main() -> int {
  i64 A;
  scanf("%" SCNd64, &A);
  i64 B;
  scanf("%" SCNd64, &B);
  i64 C;
  scanf("%" SCNd64, &C);
  i64 K;
  scanf("%" SCNd64, &K);
  solve(A, B, C, K);
  return 0;
}