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 AtCoder
{
    public class Program
    {
        public static void Main()
        {
            ulong a,b,c,k;

            string line = System.Console.ReadLine();
            string []input = line.Split(' ');
            a = ulong.Parse(input[0]);
            b = ulong.Parse(input[1]);
            c = ulong.Parse(input[2]);
            k = ulong.Parse(input[3]);
            ulong rest=0;
            if(k<=a) rest = k;
            else if(k<= a+b) rest = a;
            else {
                rest = a-(k-(a+b));
            }

            Console.WriteLine(rest);
        }

    }
}