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: Accepted)

inputs = gets.chomp.split.map!(&:to_i)
a = 0
if inputs[0] > inputs[3] then
  a += inputs[3]
elsif inputs[0] <= inputs[3] && inputs[1] > (inputs[3] - inputs[0]) then
  a += inputs[0]
else inputs[0] <= inputs[3] && inputs[1] <= (inputs[3] - inputs[0]) && inputs[2] <= (inputs[3] - inputs[0] - inputs[1])
  a += (inputs[0] - (inputs[3] - inputs[0] - inputs[1]))
end

puts a