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.AtCoder_Begginer_Contest_167
{
    class B
    {
        static void Main(string[] args)
        {
            string[] input = Console.ReadLine().Split(' ');
            int A = int.Parse(input[0]);
            int B = int.Parse(input[1]);
            int C = int.Parse(input[2]);
            int K = int.Parse(input[3]);

            int sum = CalcSum(A, B, C, K);

            Console.WriteLine(sum);
            // Console.ReadKey();
        }

        private static int CalcSum(int A, int B, int C, int K)
        {
            int k = K;
            int sum = 0;
            if (k <= A)
            {
                sum += k * 1;
                return sum;
            }
            else
            {
                sum += A;
                k = k - A;
            }

            if (k <= B)
            {
                sum += k * 0;
                return sum;
            }
            else
            {
                sum += B * 0;
                k = k - B;
            }

            if (k <= C)
            {
                sum += k * -1;
                return sum;
            }
            else
            {
                sum += C * -1;
                k = k - C;
            }

            return sum;
        }
    }
}