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.IO;
using System.Linq;

namespace AtCoder.R167.B
{
    public static class Solver
    {
        public static void Main()
        {
            using (var sw = new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false })
            {
                Solve(Console.In, sw);
            }
        }

        public static void Solve(TextReader tr, TextWriter tw)
        {
            WriteAnswer(tw, Parse(tr));
        }

        private static void WriteAnswer(TextWriter tw, int answer)
        {
            tw.WriteLine(answer);
        }

        private static int Parse(TextReader tr)
        {
            var w = tr.ReadLine().Split().Select(x => int.Parse(x)).ToArray();
            return Calc(w[0], w[1], w[2], w[3]);
        }

        public static int Calc(int a, int b, int c, int k)
        {
            var res = 0;
            if (a >= k)
                return k;
            res += a;
            k -= a;
            if (b >= k)
                return res;
            k -= b;
            return res - k;
        }
    }
}