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;

namespace AtCoder2020Ned
{
    class Program
    {
        static void Main(string[] args)
        {
            var input = Console.ReadLine().Split(" ");

            var one = int.Parse(input[0]);
            var zero = int.Parse(input[1]);
            var minusOne = int.Parse(input[2]);
            var pick = int.Parse(input[3]);

            var currentPicked = 0;
            var sum = 0;

            //for (int i = 0; one > 0 && pick > 0; i++)
            //{
            //    sum++;
            //    one--;
            //    pick--;
            //}
            //for (int i = 0; zero > 0 && pick > 0; i++)
            //{
            //    zero--;
            //    pick--;
            //}
            //for (int i = 0; minusOne > 0 && pick > 0; i++)
            //{
            //    sum--;
            //    minusOne--;
            //    pick--;
            //}

            var overOne = one - pick;
            var overZero = 0;
            if (overOne < 0)
            {
                overZero = zero + overOne;
                if (overZero > 0)
                {
                    Console.WriteLine(overOne - overZero);
                    return;
                }
                else
                {
                    Console.WriteLine(overOne);
                    return;
                }
            }
            else
            {
                Console.WriteLine(overOne);
                return;
            }

            Console.WriteLine(sum);
            Console.Read();
        }
    }
}