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.Collections.Generic;
using System.Numerics;
using System.Linq;
using System.Text;
using static System.Math;

class MainClass
{

    public static void Main(string[] args)
    {
        var _ = LnLngs();
        var A = _[0]; var B = _[1]; var C = _[2]; var K = _[3];
        if (A >= K)
        {
            print(K);
        }
        else if (A + B >= K)
        {
            print(A);
        }
        else
        {
            var min = K - A - B;
            print(A - min);
        }
    }

    public static long SumAtoB(long a, long b) { var length = b - a + 1; return (a + b) * (length / 2) + (length % 2 == 1 ? (a + b) / 2 : 0); }
    public static long PowLite(long n, long p, int mod = (int)1e9 + 7) { long ans = 1; long now = n; for (; p > 0; p >>= 1) { if ((p & 1) == 1) { ans *= now; ans %= mod; } now *= now; now %= mod; } return ans; }
    public static void print(object obj) { Console.WriteLine(obj); }
    public static long Gcd(long a, long b) { if (a > b) { var r = a % b; if (r == 0) return b; else return Gcd(b, r); } else { var r = b % a; if (r == 0) return a; else return Gcd(a, r); } }
    public static int Gcd(int a, int b) { if (a > b) { var r = a % b; if (r == 0) return b; else return Gcd(b, r); } else { var r = b % a; if (r == 0) return a; else return Gcd(a, r); } }
    public static int[] LnInts() { var vs = Console.ReadLine().Trim().Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries); var ins = new int[vs.Length]; for (int i = 0; i < vs.Length; i++) ins[i] = int.Parse(vs[i]); return ins; }
    public static int LnInt() { var vs = Console.ReadLine().Trim(); return int.Parse(vs); }
    public static long[] LnLngs() { var vs = Console.ReadLine().Trim().Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries); var ins = new long[vs.Length]; for (int i = 0; i < vs.Length; i++) ins[i] = long.Parse(vs[i]); return ins; }
    public static long LnLng() { var vs = Console.ReadLine().Trim(); return long.Parse(vs); }
    public static string[] LnStrs() { var vs = Console.ReadLine().Trim().Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries); return vs; }
    public static string LnStr() { var vs = Console.ReadLine().Trim(); return vs; }
    public static List<T[]> AllPermutation<T>(params T[] array) where T : IComparable { var a = new List<T>(array).ToArray(); var res = new List<T[]>(); res.Add(new List<T>(a).ToArray()); var n = a.Length; var next = true; while (next) { next = false; int i; for (i = n - 2; i >= 0; i--) { if (a[i].CompareTo(a[i + 1]) < 0) break; } if (i < 0) break; var j = n; do { j--; } while (a[i].CompareTo(a[j]) > 0); if (a[i].CompareTo(a[j]) < 0) { var tmp = a[i]; a[i] = a[j]; a[j] = tmp; Array.Reverse(a, i + 1, n - i - 1); res.Add(new List<T>(a).ToArray()); next = true; } } return res; }
}