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)

import sys
import math
import itertools
import collections

def solve(A,B,C,K):
    ans = 0
    while K != 0:
        if( A != 0):
            if(K < A):
                ans += K
                break
            else:
                ans+=A
                K -= A
                A = 0
        elif(B != 0):
            if(K < B):
                break
            else:
                K -= B
                B = 0
        else:
            if(K < C):
                ans -= K
                break
            else:
                ans -= C
                K -= C
                C = 0
    return ans
def main():
    A,B,C,K =map(int,input().split())
    # solve()
    print(solve(A,B,C,K))

if __name__ == "__main__":
    main()