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

namespace abc167
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.SetOut(new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false });
            if (File.Exists("input.txt"))
            {
                Console.SetIn(new StreamReader("input.txt"));
            }
            solve_abc167B();
            Console.Out.Flush();
        }

        public static void solve_abc167B()
        {
            long[] abck = Array.ConvertAll(Console.ReadLine().Split(), long.Parse);
            long a = abck[0];
            long b = abck[1];
            long c = abck[2];
            long k = abck[3];
            long max = Math.Min(a, k) - Math.Max(0, (k - a) - b);
            Console.WriteLine(max);
        }

        public static void solve_abc167A()
        {
            string a = Console.ReadLine();
            string b = Console.ReadLine();
            Console.WriteLine(a.Equals(b.Substring(0, b.Length - 1)) ? "Yes" : "No");
        }
    }
}