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 Python (3.8.2) (judge verdict: Accepted)

A, B, C, K = [int(i) for i in input().split(" ")]
N = [A, B, C]
for i in range(len(N)):
    K -= N[i]
    if K == 0:
        if i == 0:
            N[i+1] = 0
            N[i+2] = 0
        elif i == 1:
            N[i+1] = 0
        break
    elif K < 0:
        if i == 0:
            N[i+1] = 0
            N[i+2] = 0
        elif i == 1:
            N[i+1] = 0
        N[i] += K
        break
print(1 * N[0] -1 * N[2])