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;

int main(){
  long long int a,b,c,k;
  cin >> a >> b >> c >> k;
  long long count = 0;
  
  while(0 < k){
    if(a < k){count += a;k -= a;}
    else {count += k;k = 0;}
    
    if(k == 0)break;
    
    if(b < k){k -= b;}
    else {k = 0;}
    
    if(k == 0)break;
    
    if(c < k){count -= c;k -= c;}
    else {count -= k;k = 0;}
  }
  
  cout << count << endl;
}