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: Wrong Answer)

A, B, C, K = tuple(int(c) for c in input().split(' '))

if A >= K:
    print(A)
    exit()
else:
    bc = K - A  # A < K なのでbc >= 1
    #assert bc >= 1
    if B >= bc:
        if A >= C:
            print(A)
            exit()
        else:
            print(A-abs(bc-C))
    else:
        # B < bc
        cc = bc - B
        #assert cc >= 1
        print(A - cc)
        exit()