#include <string>
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
//typedef pair<long long,long long> P;
//typedef pair<long long,P> P1;
//typedef pair<P,P> P2;
#define pu push
#define pb push_back
#define mp make_pair
#define eps 1e-7
#define INF 1000000000
#define mod 1000000007
#define fi first
#define se second
#define rep(i,x) for(long long i=0;i<x;i++)
#define repn(i,x) for(long long i=1;i<=x;i++)
#define rrep(i,x) for(long long i=x-1;i>=0;i--)
#define rrepn(i,x) for(long long i=x;i>1;i--)
#define SORT(x) sort(x.begin(),x.end())
#define ERASE(x) x.erase(unique(x.begin(),x.end()),x.end())
#define POSL(x,v) (lower_bound(x.begin(),x.end(),v)-x.begin())
#define POSU(x,v) (upper_bound(x.begin(),x.end(),v)-x.begin())
long long n,h[100005];
ll dp[100005];
#define ALL(v)  (v).begin(),(v).end()
//#define MAX(a,b) if(a>b)
#define MAX(a,b) (((a)>(b))?(a):(b))
#define MIN(a,b) (((a)<(b))?(a):(b))

#define DEBUG
#define pr printf
#define re return
#define CASET int ___T, case_n = 1; scanf("%d ", &___T); while (___T-- > 0)


int GCD(int a, int b) { return b ? GCD(b, a%b) : a; }

stack<long long> sta;   
queue<long long> que;
deque<long long> dque;

set <string> s_set;

int vis[200001];

//最大公約数
int gcd(int x, int y) { return y ? gcd(y, x % y) : x; }
//最小公倍数
int lcm(int x, int y) { return x / gcd(x, y) * y; }
//最大公約数 複数個
int gcd(const vector<int> &v) {
	int ret = v[0];
	for (int i = 1; i < v.size(); i++)
		ret = gcd(ret, v[i]);
	return ret;
}
//最小公倍数 複数個
int lcm(const vector<int> &v) {
	int ret = v[0];
	for (int i = 1; i < v.size(); i++)
		ret = lcm(ret, v[i]);
	return ret;
}

struct Student {
  string name;
  int no, point;
};

// a < b ならtrueを返す
bool comp(const Student& a, const Student& b) {
  if (a.name != b.name)
    return a.name < b.name; // 高い順に並べたいので演算子を逆に
  if (a.point != b.point)
    return a.point > b.point; // 同様に比較演算子を反転
  return a.no < b.no;
}

std::string replaceOtherStr(std::string &replacedStr, std::string from, std::string to) {
    const unsigned int pos = replacedStr.find(from);
    const int len = from.length();
 
    if (pos == std::string::npos || from.empty()) {
        return replacedStr;
    }
 
    return replacedStr.replace(pos, len, to);
}


//	素因数分解
void countPN(int n, std::vector<int> &count)//nを素因数に分解し、countを更新
{
	int m = n;
	for(int i=2 ; i*i<=n ; ++i)
	{
		while(m%i == 0)
		{
			m /= i;
			count[i]++;
		}
		if(m==1) break;
	}
	if(m!=1) count[m]++;

}

int main(){
	
	long long A,B,C,D,E,F,G,H,I,J,L,N,M,K,O,P,Q,R,S,T,U,V,W,X,Y,Z;
	long long sum,sum1,sum2,sum3,sum4;
	sum=sum1=sum2=sum3=sum4=0;
	long long flg,flg1,flg2,flg3,cnt,cnt1,cnt2,cnt3,cnt4;
	flg=flg1=flg2=flg3=cnt=cnt1=cnt2=cnt3=cnt4=0;
	long long max;
	long long max1;
	max=max1=0;
	long long min;
	long long min1;
	min=min1=INF;
	long long wk,wk1,wk2,wk3,wk4;
	wk=wk1=wk2=wk3=wk4=0;
    bool f;
	ll ans=0;
	
	
	//std::cin >> N;
	std::cin >> N >> T;
	std::vector<long long> v(N);
    
	// 配列入力1
	
	for(long long i=0; i<N; i++){
		std::cin >> v[i];
	}
		
	
	//std::sort(v.begin(),v.end());//昇順ソート
	//std::sort(v.begin(),v.end(),std::greater<long long>());//降順ソート
	
	//通常
	
	for(long long i=0; i<N-1; i++){
		if(v[i+1]-v[i]<T){
			sum+=T-(v[i+1]-v[i]);
		}
	}
	pr("%lld",N*T-sum);
	re 0;

}


Measured memory_bytes: 1792