C++ :

#include<bits/stdc++.h>
using namespace std;
long long n,t,x,a1,b1,a2,b2,ans;
int main()
{
//	freopen("590.in","r",stdin);
//	freopen("590.out","w",stdout);	
	cin>>n>>t>>x;
	a1=x,b1=x+t-1;
	ans=b1-a1+1;
	for(int i=1;i<n;i++)
	{
		cin>>x;
		a2=x,b2=x+t-1;
		if(a2>b1) ans+=t;
		else ans+=t-(b1-a2+1);
		a1=a2,b1=b2;
	}
	cout<<ans;
	return 0;
}