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: Accepted)

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

namespace easy_Atcoder
{
    class Program
    {
        static void Main(string[] args)
        {
            // float[] ABN = Array.ConvertAll(Console.ReadLine().Split(),float.Parse);
            int[] ABCK = Array.ConvertAll(Console.ReadLine().Split(),int.Parse);
            // long K = long.Parse(Console.ReadLine());
            // int[] abc = Array.ConvertAll(Console.ReadLine().Split(),int.Parse);
            // string S = Console.ReadLine();
            // int a = int.Parse(Console.ReadLine());
            // int b = int.Parse(Console.ReadLine());
            // int h = int.Parse(Console.ReadLine());
            // float N = float.Parse(Console.ReadLine());
            // string c = Console.ReadLine();
            // string B = Console.ReadLine();
            // string[] AopB = Console.ReadLine().Split();
            // var s = (new string[] { Console.ReadLine(), Console.ReadLine(), Console.ReadLine() }).Select(float.Parse);
            // float[] a = Array.ConvertAll(Console.ReadLine().Split(),float.Parse);
            // var X = Console.ReadLine();
            // int[,] abcd = new int[NMQ[2],4];
            // int[] A = new int[NMQ[0]];
            // int[] A_num = new int[NMQ[0]];
            // long[] s=Array.ConvertAll(Console.ReadLine().Split(),long.Parse);
            // var hs=new Dictionary<long,long>();
            // for(int i=0;i<s[0];i++){
            //     long[] q=Array.ConvertAll(Console.ReadLine().Split(),long.Parse);
            //     if(hs.ContainsKey(q[0])){hs[q[0]]+=q[1];}
            //     else{hs.Add(q[0],q[1]);}
            // }
            // List<long> kl=new List<long>(hs.Keys);
            // kl.Sort();
            // foreach(long k in kl){
            //     s[1]-=hs[k];
            //     if(s[1]<1){Console.WriteLine("{0}",k);break;}
            // }
            long sum = 0;
            if(ABCK[0]>=ABCK[3]){
                sum+=ABCK[3]*1;
            }else{
                sum+=1*ABCK[0];
                ABCK[3] = ABCK[3]-ABCK[0];
                if(ABCK[3]>=ABCK[1]){
                    ABCK[3] = ABCK[3]-ABCK[1];
                    sum += -1*ABCK[3];
                }else{
                    sum+=0;
                }
            }
            Console.WriteLine(sum);

        }
        //最小公倍数
        static long Lcm(long a, long b)
        {
            return a/Gcd(a,b)*b;
        }

        //最大公約数
        static long Gcd(long m, long n)
        {
            if(n==0)return m;
            return Gcd(n,m%n);
        }
    }
}