#include <bits/stdc++.h>
using namespace std;

typedef long lint;
typedef long long llint;
typedef pair<int, int> pint;
typedef pair<long long, long long> pllint;

// static const int MAX = 1e6;
// static const int NIL = -1;
// static const llint INF = 1<<21;
// static const llint MOD = 1e9 + 7;

bool compPair(const pint& arg1, const pint& arg2) { return arg1.first > arg2.first; }
template<class T> void chmax(T& a, T b) { if (a < b) { a = b; } }
template<class T> void chmin(T& a, T b) { if (a > b) { a = b; } }

int main(void) {
    int n, t;
    cin >> n >> t;

    int ans = 0, tnow, tpush, tbfr;
    cin >> tbfr;
    for(int in=1;in<n;in++) {
        cin >> tpush;
        if(tpush-tbfr<=t) ans += tpush-tbfr;
        else ans += t;
        tbfr = tpush;
    }
    ans += t;
    cout << ans << endl;
    return 0;
}

#include <bits/stdc++.h>
#include <climits>
#include <cmath>
#include <iomanip>
#include <math.h>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
//#define local
#ifdef local
    #include "dbg-macro/dbg.h"
#endif
//#define hacks
#ifdef hacks
    #include <boost/multiprecision/cpp_int.hpp>
#endif
#define p std::pair
#define ll long long
#define ld long double
#define ull unsigned long long
#define pi std::pair<int, int>
#define stdabs std::abs
#define all(x) (x).begin(), (x).end()
#define rep(i, n) for (unsigned long long i = 0; i < (unsigned long long)(n); ++i)
#define vec std::vector
#define oreq |=
#define npm next_permutation
using namespace std;
std::vector<unsigned ll> genprimevec(const unsigned ll N);
ll extgcd(ll a, ll b, ll& x, ll& y);
ll nCr(ll n, ll r);
void stat();
template <typename T> T fact(T num);
constexpr ll mod = 1000000000 + 7;
int main()
{
    stat();
    ll n, t;
    cin >> n >> t;
    ull ans = 0,curtime=0;
    vec<ll> v(n);
    rep(i, n) { cin >> v[i]; }
    rep(i,n-1){
	    curtime+=v[i];
	    ans+=min(t,abs(v[i+1]-v[i]));
    }
    cout<<ans+t<<endl;
    return 0;
}
ll extgcd(ll a, ll b, ll& x, ll& y)
{
    if (b == 0) {
        x = 1, y = 0;
        return a;
    }
    ll d = extgcd(b, a % b, y, x);
    y -= a / b * x;
    return d;
}


std::vector<unsigned ll> genprimevec(const unsigned ll N)
{
    std::vector<bool> is_prime(N + 1);
    for (unsigned ll i = 0; i <= N; i++) {
        is_prime[i] = true;
    }
    std::vector<unsigned ll> P;
    for (unsigned ll i = 2; i <= N; i++) {
        if (is_prime[i]) {
            for (unsigned ll j = 2 * i; j <= N; j += i) {
                is_prime[j] = false;
            }
            P.emplace_back(i);
        }
    }
    return P;
}

void stat(){
#ifdef local
    rep(i, 2){std::cout << "local enable" << std::endl;
}
#endif
#ifdef hacks
rep(i, 2) { std::cout << "boost enable" << std::endl; }
#endif
}

ll nCr(ll n, ll r)
{
    ll num = 1;
    for (ll i = 1; i <= r; i++) {
        num = num * (n - i + 1) / i;
    }
    return num;
}

template <typename T> T fact(T num)
{
    if (num == 1) { return 1; }
    return num * fact(num - 1);
}
