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)  # スペースで区切られた複数の整数
sum = 0

# calc a
sum = sum + a * 1
b_and_c_nokori = k - a

if b_and_c_nokori == 0 # finish
else
  if b_and_c_nokori < b then  sum += 0
  else sum += (b_and_c_nokori - b)  * -1
  end
end

puts sum