Solve in Python:
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-----
2 1 1 3

-----Sample Output-----
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.
A, B, C, K = list(map(int, input().split()))

a, c = min(A, K), max(0, min(C, K - A - B))
print((a - c))