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 PHP (7.4.4) (judge verdict: Wrong Answer)

<?php
  
  fscanf(STDIN, "%d %d %d %d", $A, $B, $C, $K);
	
	$a = $K - $A;
	if($a <= 0){
    	echo 1*$A;
    }elseif($a > 0){
      	$b = $a - $B;
      	if($b <= 0){
        	echo 1*$A;
        }elseif($b > 0 ){
        	echo 1*$A + (-1*$b);
        }
    }
echo "\n";