using System;

using System.Linq;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

    }

    public static int solution(int[] A) {

        // write your code in C# 6.0 with .NET 4.5 (Mono)

        var ordered = A.OrderBy(n => n);

        //Console.WriteLine(String.Join(",",ordered));

        var step = ordered.Skip(1);

        //Console.WriteLine(String.Join(",",step));

        return ordered.Zip(step, (a,b) => new {left= a, right = b, diff =b - a}).First(x => x.diff > 1).right - 1;

    }

}