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 Kotlin (1.3.71) (judge verdict: Wrong Answer)

fun main(args: Array<String>) {
    val (A, B, C, K) = readLine()!!.split(" ").map { it.toLong() }

    fun calcElems(elemNums: List<Long>, amount: Long, calcResult: List<Long> = listOf(), index: Int = 1): List<Long> {
        val targetNum = elemNums.first()
        val (newAmount, newElemNum) = if (amount > targetNum) Pair(amount - targetNum, targetNum) else Pair(0L, amount)
        val newResult = calcResult.plusElement(newElemNum)

        return if (elemNums.size == index) newResult else calcElems(elemNums, newAmount, newResult, index + 1)
    }
    val (a, _, c) = calcElems(listOf(A, B, C), K)

    println(a - c)
}