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 Ruby (2.7.1) (judge verdict: Wrong Answer)

a,b,c,k = gets.split(" ").map(&:to_i)
a = a.to_i
b = b.to_i
c = c.to_i
$k = k.to_i

def count(x,k,point)
    return 0 if $k == 0
    case $k <=> x
    when 1 then
        $k = $k - x
        return point * x
    when 0 then
        $k = 0
        return point * x
    when -1 then
        return point * $k
        $k = 0
    end
end

puts count(a,k,1) + count(b,k,0) + count(c,k,-1)