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-csc 3.5.0) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main(string[] args)
    {
        new Program();
    }

    Program()
    {
        var abck = Console.ReadLine().Split(' ');
        var a = long.Parse(abck[0]);
        var b = long.Parse(abck[1]);
        var c = long.Parse(abck[2]);
        var k = long.Parse(abck[3]);

        var aa = Math.Min(a, k);
        k -= aa;
        var bb = Math.Min(b, k);
        k -= bb;
        var cc = Math.Min(c, k);

        Console.WriteLine(aa - cc);
    }
}