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<iostream>
#include<vector>
#include<algorithm>
#include<cmath>
#include<ctime>
#include<queue>

using namespace std;
using ll = long long;
using vi = vector<int>;
using vvi = vector<vector<int> >;
using pii = pair<int, int>;
using ppi = pair<pii, int>;

int f_dir[2][4] = {{-1, 0, 1, 0}, {0, 1, 0, -1}}; //↑→↓←
int e_dir[2][8] = {{-1, -1, -1, 0, 0, 1, 1, 1}, {-1, 0, 1, -1, 1, -1, 0, 1}};
bool is_in_field(int y, int x, int h, int w){
  return (y >= 0 && y < h && x >= 0 && x < w);
}

int main(){
  cin.tie(0);
  ios::sync_with_stdio(false);
  int ti = clock();
  // start-----------------------------------------------
  ll a, b, c, k;
  cin >> a >> b >> c >> k;
  int p = min(k, a);
  k -= a;
  int z = max(ll(0), min(k, b));
  k -= b;
  int m = max(ll(0), min(k, c));
  cout << p - m << endl;

  // end-----------------------------------------------
  // cerr << 1.0 * (clock() - ti) / CLOCKS_PER_SEC << endl;
}