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)

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


a_num = 0
b_num = 0
c_num = 0

if k - a > 0
  a_num = a
  if (k - a) -b > 0
    b_num = b
    if (k -a -b)-c > 0
      c_num = c

    else
      c_num = k-a-b
    end
  else
    b_num = k-a
  end
else
  a_num = k
end


puts a_num * 1 + c_num * -1