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.chomp.split.map(&:to_i)

a = 0
b = 0
c = 0

if A <= K then
  a = A
  if A + B <= K then
    b = B
    if A + B + C <= K then
      c = C
    end
  end
end
while (a + b + c) < K do
  if a + 100000 < A && A < K then
    a += 100000
  elsif b + 100000 < B  && B < K then
    b += 100000
  elsif c + 100000 < C  && C < K then
    c += 100000
  end
end 
while (a + b + c) < K do
  if a < A then
    a += 1
  elsif b < B then
    b += 1
  elsif c < C then
    c += 1
  end
end
    
puts a - c