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)

# -*- coding: utf-8 -*-
from sys import stdin
from operator import itemgetter
from collections import deque, Counter
import math
import pprint
from functools import reduce
# stdin = open("sample.txt")

MOD = 1000000007

def keta(kazu):
    kazu_str = str(kazu)
    kazu_list = [int(kazu_str[i]) for i in range(0, len(kazu_str))]
    return kazu_list

def gcd(*numbers):
    return reduce(math.gcd, numbers)

def combination(m,n):
    if n > m:
        return 'すまん'
    return math.factorial(m) // (math.factorial(m-n) * math.factorial(n))

def main():
    a, b, c, k = [int(x) for x in stdin.readline().rstrip().split()]
    if a >= k:
        print(k)
    elif a + b >= k:
        print(a)
    else:
        nokori = k - (a + b)
        print(a - nokori)

main()