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# (Mono-mcs 6.8.0.105) (judge verdict: Wrong Answer)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace TOPSIC2
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] ABCK = Console.ReadLine().Split(' ');
            long A = long.Parse(ABCK[0]);
            long B = long.Parse(ABCK[1]);
            long C = long.Parse(ABCK[2]);
            long K = long.Parse(ABCK[3]);

            long ans = 0;

            if (A <= K)
            {
                ans += A;

                if (A + B <= K)
                {
                    ans -= K - A - B;
                }
            }
            else
            {
                ans = A;
            }

            Console.WriteLine(ans);
        }
    }
}