// C++ includes used for precompiling -*- C++ -*-

// Copyright (C) 2003-2013 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.

/** @file stdc++.h
 *  This is an implementation file for a precompiled header.
 */

// 17.4.1.2 Headers

// C
//デバッグ用オプション：-fsanitize=undefined,address

//コンパイラ最適化
#pragma GCC optimize("Ofast")
#ifndef _GLIBCXX_NO_ASSERT
#include <cassert>
#endif
#include <cctype>
#include <cerrno>
#include <cfloat>
#include <ciso646>
#include <climits>
#include <clocale>
#include <cmath>
#include <csetjmp>
#include <csignal>
#include <cstdarg>
#include <cstddef>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>

#if __cplusplus >= 201103L
#include <ccomplex>
#include <cfenv>
#include <cinttypes>
#include <cstdbool>
#include <cstdint>
#include <ctgmath>
#include <cwchar>
#include <cwctype>
#endif

// C++
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <typeinfo>
#include <utility>
#include <valarray>
#include <vector>

#if __cplusplus >= 201103L
#include <array>
#include <atomic>
#include <chrono>
#include <condition_variable>
#include <forward_list>
#include <future>
#include <initializer_list>
#include <mutex>
#include <random>
#include <ratio>
#include <regex>
#include <scoped_allocator>
#include <system_error>
#include <thread>
#include <tuple>
#include <typeindex>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
#endif

/*全てのライブラリをインクルード*/
using namespace std;
using ll = long long;
//マクロ
//forループ
//引数は、(ループ内変数,動く範囲)か(ループ内変数,始めの数,終わりの数)、のどちらか
//Dがついてないものはループ変数は1ずつインクリメントされ、Dがついてるものはループ変数は1ずつデクリメントされる
//FORAは範囲for文(使いにくかったら消す)
#define rep(i, n) for (ll i = 0; i < ll(n); i++)
#define REPD(i, n) for (ll i = n - 1; i >= 0; i--)
#define FOR(i, a, b) for (ll i = a; i <= ll(b); i++)
#define FORD(i, a, b) for (ll i = a; i >= ll(b); i--)
#define FORA(i, I) for (const auto &i : I)
//xにはvectorなどのコンテナ
#define ALL(x) x.begin(), x.end()
#define SIZE(x) ll(x.size())
//定数
#define INF 1000000000000 //10^12:∞
#define MOD 1000000007    //10^9+7:合同式の法
#define MAXR 100000       //10^5:配列の最大のrange
//略記
#define PB push_back //挿入
#define MP make_pair //pairのコンストラクタ
#define F first      //pairの一つ目の要素
#define S second     //pairの二つ目の要素

signed main()
{
    //入力の高速化用のコード
    //ios::sync_with_stdio(false);
    //cin.tie(nullptr);
    ll n, t;
    cin >> n >> t;
    ll count = 0;
    ll time = 0;
    rep(i, n)
    {
        int t_i;
        cin >> t_i;
        if (i == 0)
        {
            count += t;
            time = t_i;
        }
        else
        {
            if (t_i - time < t)
            {
                count -= t - t_i + time;
                count += t;
                time = t_i;
            }
            else
            {
                count += t;
                time = t_i;
            }
        }
    }
    cout << count << endl;
    return 0;
}

Measured memory_bytes: 3604