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?

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.

Constraints

• All values in input are integers.
• $0 \leq A, B, C$
• $1 \leq K \leq A + B + C \leq 2 \times 10^9$

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

见题面 Input 部分

见题面 Output 部分