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: Runtime Error)

a, b, c, k = gets.split(" ").map(&:to_i)
plus = Array.new(a, 1)
zero = Array.new(b, 0)
minus = Array.new(c, -1)
count = k
sum = 0
while a > 0 && k > 0
  sum += 1
  a -= 1
  k -= 1
end
while b > 0 && k > 0
  b -= 1
  k -= 1
  end
while c > 0 && k > 0
  sum += -1
  c -= 1
  k -= 1
end
p sum