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);
/*
$a(+1)が0になるまで$aを引き、
$aが0になったらなったら$b(+0)が0になるまで引き、
$bが0になったら$c(-1)を0になるまで引く
*/
$n = 0; //出力値を初期化

// $K-$aが0以下だったら$nは1*$a
// $K-$aが1以上、かつ$K-$bが0以下だったら$nは1*$a (+ 0*$b) ※0*$bは0なので無視
// $K-$aが1以上、かつ$K-$bが1以上だったら$nは1*$a + (-1)*$c (+ 0*$b)

if($K-($a+$b) < 1){
    $n = $a;
}else{
    $n = $a + (-1 * ($K-($a+$b)));
}
echo $n;
?>