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 C# (.NET Core 3.1.201) (judge verdict: Accepted)

using System;

namespace ABC167B
{
    class Program
    {
        static void Main(string[] args)
        {
            var target = Console.ReadLine().Split(' ');
            long A = long.Parse(target[0]);
            long B = long.Parse(target[1]);
            long C = long.Parse(target[2]);
            long K = long.Parse(target[3]);
            long max = 0;
            if(K <= A) max = K;
            else if(K <= A+B) max = A;
            else max = A-(K-(A+B));
            Console.WriteLine(max);
        }
    }
}