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;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace AtCoder.Abc
{
    class QuestionB
    {
        /// <summary>
        /// B - Easy Linear Programming
        /// https://atcoder.jp/contests/abc167/tasks/abc167_b
        /// </summary>
        /// <param name="args"></param>

        public static void Main(string[] args)
        {
            var sw = new System.IO.StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
            Console.SetOut(sw);

            // 文字列配列の入力
            int[] str_ABCK = Console.ReadLine().Split(' ').Select(i => int.Parse(i)).ToArray();
                        
            int result = 0;

            if (str_ABCK[3] <= str_ABCK[0])   //引く枚数がＡより少ないときは引く枚数が答え
            {
                result = str_ABCK[3];
            }
            else if (str_ABCK[3] <= str_ABCK[0] + str_ABCK[1])
            {
                result = str_ABCK[0];
            }
            else
            {
                //マイナスカードの枚数
                int num_Minus = str_ABCK[3] - (str_ABCK[0] + str_ABCK[1]);
                result = str_ABCK[0] - num_Minus;
            }
            


            Console.WriteLine(result);

            Console.Out.Flush();
        }
    }
}