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# (Mono-mcs 6.8.0.105) (judge verdict: Accepted)

using System;

namespace ABC167B
{
    class Program
    {
        static void Main(string[] args)
        {
            var input = Console.ReadLine().Split(' ');
            var a = int.Parse(input[0]);
            var b = int.Parse(input[1]);
            var c = int.Parse(input[2]);
            var k = int.Parse(input[3]);

            var result = 0;
            if (k > 0)
            {
                if (a > 0 && a <= k)
                {
                    result = result + a * 1;
                    k = k - a;
                }
                else if (a > k)
                {
                    result = result + k * 1;
                    k = 0;
                }
            }

            if (k > 0)
            {
                if (b > 0 && b <= k)
                {
                    k = k - b;
                }
                else if (b > k)
                {
                    k = 0;
                }
            }

            if (k > 0)
            {
                if (c > 0 && c <= k)
                {
                    result = result + (c * (-1));
                    k = k - c;
                }
                else if (c > k)
                {
                    result = result + k * (-1);
                    k = 0;
                }
            }
            Console.WriteLine(result);
        }
    }
}