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: Accepted)

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

namespace Atcoder_Answer
{
    class Program
    {
        const Int32 mod = 1000000007;

        static void Main(string[] args)
        {
            string[] Reader = ReadLine().Split(' ');

            int A = int.Parse(Reader[0]);
            int B = int.Parse(Reader[1]);
            int C = int.Parse(Reader[2]);
            int K = int.Parse(Reader[3]);

            if (A > K)
            {
                WriteLine(K);
                return;
            }
            else 
            {
                WriteLine(A + Math.Max(0, K - A - B) * -1);
                return;
            }
        }

        #region Functions
        public static decimal floor(float d) => Math.Floor((decimal)d);

        public static double nqrt(int n, int value) 
        {
            if (n >= 0)
            {
                // 通常のn乗根
                return Math.Pow(n, 1.0 / (double)n);
            }
            else
            {
                if ((n % 2) != 0)
                {
                    // 奇数乗根の場合
                    return -Math.Pow(-n, 1.0 / (double)n);
                }
                else
                {
                    // 偶数乗根の場合
                    return double.NaN;
                }
            }
        }
        #endregion
    }

    public static class Extension
    {
        #region 拡張:bool
        #region キャスト関連
        public static int ToInt(this bool Bool)
        {
            if (Bool) return 1;
            else return 0;
        }

        public static string ToString(this bool Bool, string TrueStr, string FalseStr)
        {
            if (Bool) return TrueStr;
            else return FalseStr;
        }
        #endregion
        #endregion

        #region 拡張:int
        #region キャスト関連
        public static char ToAlphaBets(this int Base) => (char)Base;
        #endregion
        #endregion

        #region 拡張:char
        #region 変換関連
        public static char NextAlpha(this char Char) => (char)((Char) + 1); //次の文字を取得
        #endregion
        #endregion

        #region 拡張:int[]
        public static long Sum(this int[] Array)
        {
            int Ret = 0;
            for (int loop = 0; loop < Array.Length; loop++) Ret += Array[loop];
            return Ret;
        }
        #endregion

        #region 拡張: string
        public static string Multi(this string THIS, int Value)
        {
            string RetValue = "";

            for (int loop = 0; loop < Value; loop++) RetValue += THIS;

            return RetValue;
        }
        #endregion

        #region 拡張: List<string>
        public static string Sum(this List<string> THIS, string Split)
        {
            string RetValue = "";

            for (int loop = 0; loop < THIS.Count; loop++)
            {
                RetValue += THIS[loop];
            }

            return RetValue;
        }
        #endregion
    }
}