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-csc 3.5.0) (judge verdict: Wrong Answer)

    using System;
    using System.Linq;
    using System.Collections.Generic;
    using System.IO;
    using System.Text;

    class Program
    {
        static void Main()
        {
            var inputList = Console.ReadLine().Split(' ').ToList();
            var a = inputList[0].ToInt32();
            var b = inputList[1].ToInt32();
            var c = inputList[2].ToInt32();
            var k = inputList[3].ToInt32();
            var ans = 0;
            if (a >= k)
            {
                ans += a;
            }
            if (a + b < k)
            {
                ans -= k - a - b;
            }

            Console.WriteLine(ans.ToString());
        }
    }
    static class Extentions
    {
        #region 拡張メソッド（string）

        public static string LeftB(this string stTarget, int iByteSize)
        {
            return MidB(stTarget, 1, iByteSize);
        }

        public static string MidB(this string stTarget, int iStart)
        {
            System.Text.Encoding hEncoding = System.Text.Encoding.GetEncoding("utf-8");
            byte[] bBytes = hEncoding.GetBytes(stTarget);

            return hEncoding.GetString(bBytes, iStart - 1, bBytes.Length - iStart + 1);
        }

        public static string MidB(this string stTarget, int iStart, int iByteSize)
        {
            System.Text.Encoding hEncoding = System.Text.Encoding.GetEncoding("utf-8");
            byte[] bBytes = hEncoding.GetBytes(stTarget);

            return hEncoding.GetString(bBytes, iStart - 1, iByteSize);
        }

        public static string RightB(this string stTarget, int iByteSize)
        {
            System.Text.Encoding hEncoding = System.Text.Encoding.GetEncoding("utf-8");
            byte[] bBytes = hEncoding.GetBytes(stTarget);

            return hEncoding.GetString(bBytes, bBytes.Length - iByteSize, iByteSize);
        }

        public static bool IsNullOrEmpty(this string str)
        {
            return string.IsNullOrEmpty(str);
        }

        /// <summary>
        /// カルチャに依存した比較、または大文字と小文字を区別しない比較などの序数による比較を指定できる Contains。
        /// </summary>
        /// <param name="value">対象文字列</param>
        /// <param name="partialValue">部分文字列</param>
        /// <param name="comparison">カルチャ、大文字と小文字の区別、および並べ替え規則を指定する StringComparison</param>
        /// <returns>一致する場合に true を返します。</returns>
        public static bool Contains(this string value, string partialValue, StringComparison comparison = 0)
        {
            return value.IndexOf(partialValue, comparison) >= 0;
        }

        public static bool IsNumeric(this string value)
        {
            return decimal.TryParse(value, out decimal d);
        }
        public static int ToInt32(this String number, int retValue = 0)
        {
            if (!number.IsNumeric()) return retValue;
            return int.Parse(number);
        }

        #endregion
    }