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.Collections.Generic;

namespace Atc_0020
{
    class Program
    {
        static void Main(string[] args)
        {
            var s = Console.ReadLine();

            ulong A = ulong.Parse(s.Split(' ')[0]);
            ulong B = ulong.Parse(s.Split(' ')[1]);
            ulong C = ulong.Parse(s.Split(' ')[2]);
            ulong K = ulong.Parse(s.Split(' ')[3]);

            ulong ans = 0;

            if (A == K)
            {
                Console.WriteLine(A);
                return;
            }

            for (ulong i = 0; i < K; i++)
            {
                if (0 < A)
                {
                    ans++;
                    A--;

                    continue;
                }

                if (0 < B)
                {
                    i += B;
                    B = 0;
                    continue;
                }

                if (0 < C)
                {
                    ans--;
                    C--;

                    continue;
                }
            }

            Console.WriteLine(ans);

        }
    }
}