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

namespace Contest
{
    class Program
    {
        static void Main(string[] args)
        {
            ARC073.C();
        }
        class ARC073
        {
            public static void C()
            {
                var N = Read.Int();
                var T = Read.Long();
                var t = Read.LongN();
                long total = 0;
                for(int i = 0; i < N; ++i)
                {
                    total += i == 0 ? T : Math.Min(T, t[i] - t[i - 1]); 
                }
                Console.WriteLine(total);
            }
            public static void D()
            {
                var N = Read.Int();
                var W = Read.Long();
                var WV = Read.TupleLong(N);
                var w0 = WV[0].Item1;
                var dp = Util.Gen(301, N + 1, (long)-1e18);
                for(int i = 0; i <= 300; ++i) { dp[i, 0] = 0; }
                for(int i = 0; i < N; ++i)
                {
                    var w = WV[i].Item1 - w0;
                    var v = WV[i].Item2;
                    for(int n = i; n >= 0; --n)
                    {
                        for (int z = 0; z <= i * 3; ++z)
                        {
                            dp[z + w, n + 1] = Math.Max(dp[z + w, n + 1], dp[z, n] + v);
                        }
                    }
                }
                long max = 0;
                for(int n = 1; n <= N; ++n)
                {
                    var w = W - w0 * n;
                    if (w < 0) { continue; }
                    for (int i = 0; i <= Math.Min(300, w); ++i)
                    {
                        max = Math.Max(max, dp[i, n]);
                    }
                }
                Console.WriteLine(max);
            }
        }
        class Util
        {
            public static T[,] Gen<T>(int r, int c, T v)
            {
                var matrix = new T[r, c];
                for (int i = 0; i < r; ++i)
                {
                    for (int j = 0; j < c; ++j)
                    {
                        matrix[i, j] = v;
                    }
                }
                return matrix;
            }
        }

        static class Read
        {
            static Queue<string> queue = new Queue<string>();
            static void Enqueue() { var ss = Console.ReadLine().Split(' '); foreach (var s in ss) { queue.Enqueue(s); } }
            public static int Int() { if (queue.Count == 0) { Enqueue(); } return Convert.ToInt32(queue.Dequeue()); }
            public static long Long() { if (queue.Count == 0) { Enqueue(); } return Convert.ToInt64(queue.Dequeue()); }
            public static string Str() { if (queue.Count == 0) { Enqueue(); } return queue.Dequeue(); }
            public static int[] IntN() { return Console.ReadLine().Split(' ').Select(s => Convert.ToInt32(s)).ToArray(); }
            public static long[] LongN() { return Console.ReadLine().Split(' ').Select(s => Convert.ToInt64(s)).ToArray(); }
            public static ulong[] ULongN() { return Console.ReadLine().Split(' ').Select(s => Convert.ToUInt64(s)).ToArray(); }
            public static string[] StrN() { return Console.ReadLine().Split(' '); }
            public static Tuple<int, int>[] TupleInt(int n) { List<Tuple<int, int>> list = new List<Tuple<int, int>>(); for (int i = 0; i < n; ++i) { var ab = Read.IntN(); list.Add(new Tuple<int, int>(ab[0], ab[1])); } return list.ToArray(); }
            public static Tuple<long, long>[] TupleLong(int n) { List<Tuple<long, long>> list = new List<Tuple<long, long>>(); for (int i = 0; i < n; ++i) { var ab = Read.LongN(); list.Add(new Tuple<long, long>(ab[0], ab[1])); } return list.ToArray(); }
            public static Tuple<string, string>[] TupleStr(int n) { List<Tuple<string, string>> list = new List<Tuple<string, string>>(); for (int i = 0; i < n; ++i) { var ab = Read.StrN(); list.Add(new Tuple<string, string>(ab[0], ab[1])); } return list.ToArray(); }
            public static Tuple<double, double>[] TupleDouble(int n) { List<Tuple<double, double>> list = new List<Tuple<double, double>>(); for (int i = 0; i < n; ++i) { var ab = Read.LongN(); list.Add(new Tuple<double, double>(ab[0], ab[1])); } return list.ToArray(); }
            public static long[,] LongMatrix(int r, int c)
            {
                var mat = new long[r, c];
                for (int i = 0; i < r; ++i)
                {
                    var x = Read.LongN();
                    for (int j = 0; j < c; ++j)
                    {
                        mat[i, j] = x[j];
                    }
                }
                return mat;
            }
            public static Dictionary<int, HashSet<int>> AdjacencyList(int N, int M, bool isDirectional = false)
            {
                Dictionary<int, HashSet<int>> dict = new Dictionary<int, HashSet<int>>();
                for (int i = 0; i <= N; ++i) { dict.Add(i, new HashSet<int>()); }
                for (int i = 0; i < M; ++i)
                {
                    var ab = Read.IntN(); dict[ab[0]].Add(ab[1]);
                    if (!isDirectional) { dict[ab[1]].Add(ab[0]); }
                }
                return dict;
            }
            public static Dictionary<int, Dictionary<int, long>> AdjacencyListWithWeight(int N, int M)
            {
                Dictionary<int, Dictionary<int, long>> dict = new Dictionary<int, Dictionary<int, long>>();
                for (int i = 0; i <= N; ++i)
                {
                    dict.Add(i, new Dictionary<int, long>());
                }
                for (int i = 0; i < M; ++i)
                {
                    var ab = Read.IntN();
                    dict[ab[0]].Add(ab[1], ab[2]);
                    dict[ab[1]].Add(ab[0], ab[2]);
                }
                return dict;
            }
        }
    }
}


Measured memory_bytes: 31136