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: Wrong Answer)

using System;
using System.Linq;
using System.Collections.Generic;
using System.Text;
    public class Program
    {
        public static void Main(string[] args)
        {
            new B().test();
        }
    }
	public class B
	{
		public void test()
		{
			// N人とK種類
			var cards = CommonRead.ReadIntL();

			// KよりもAの数が多い場合はAだけ計算する
			if(cards[3] < cards[0])
			{
				Console.WriteLine(cards[0]);

				// KよりもA+Bの数が多い場合はAだけ計算する
			}
			else if (cards[3] < cards[0] + cards[1])
			{
				Console.WriteLine(cards[0]);
			}
			// KよりもA+B+Cの数が多い場合はA-Cを計算する
			else
			{
				var exec = cards[3] - cards[0] - cards[1] - cards[2];

				// もし0よりうえならA-C計算
				if(exec > 0)
				{
					Console.WriteLine(cards[0] - cards[2]);
				}
				else
				{
					var minus = cards[3] - cards[0] - cards[1];

					Console.WriteLine(cards[0] - minus);
				}


			}

		}
	}

static class CommonRead
{
    public static string ReadStr()
    {
        return Console.ReadLine();
    }
    public static string[] ReadStrA()
    {
        return ReadStr().Split(' ');
    }
    public static List<string> ReadStrL()
    {
        return ReadStrA().ToList();
    }
    public static int ReadInt()
    {
        return Convert.ToInt32(ReadStr());
    }
    public static int[] ReadIntA()
    {
        return ReadStrA().Select(s => Convert.ToInt32(s)).ToArray();
    }
    public static List<int> ReadIntL()
    {
        return ReadStrA().Select(s => Convert.ToInt32(s)).ToList();
    }
    public static long ReadLong()
    {
        return Convert.ToInt64(ReadStr());
    }
    public static long[] ReadLongA()
    {
        return ReadStrA().Select(s => Convert.ToInt64(s)).ToArray();
    }
    public static List<long> ReadLongL()
    {
        return ReadStrA().Select(s => Convert.ToInt64(s)).ToList();
    }

    public static decimal ReadDecimal()
    {
        return Convert.ToDecimal(ReadStr());
    }
    public static decimal[] ReadDecimalA()
    {
        return ReadStrA().Select(s => Convert.ToDecimal(s)).ToArray();
    }
    public static List<decimal> ReadDecimalL()
    {
        return ReadStrA().Select(s => Convert.ToDecimal(s)).ToList();
    }

    public static double ReadDouble()
    {
        return Convert.ToDouble(ReadStr());
    }
    public static double[] ReadDoubleA()
    {
        return ReadStrA().Select(s => Convert.ToDouble(s)).ToArray();
    }
    public static List<double> ReadDoubleL()
    {
        return ReadStrA().Select(s => Convert.ToDouble(s)).ToList();
    }

}