import std.algorithm, std.container, std.conv, std.math, std.range, std.typecons, std.stdio, std.string;

auto rdsp(){return readln.splitter;}
void pick(R,T)(ref R r,ref T t){t=r.front.to!T;r.popFront;}
void readV(T...)(ref T t){auto r=rdsp;foreach(ref v;t)pick(r,v);}
void readA(T)(size_t n,ref T[]t){t=new T[](n);auto r=rdsp;foreach(ref v;t)pick(r,v);}

void main()
{
  int n, tc; readV(n, tc);
  int[] t; readA(n, t);

  auto ans = 0;
  foreach (i; 0..n-1)
    ans += t[i+1]-t[i] > tc ? tc : t[i+1]-t[i];
  ans += tc;

  writeln(ans);
}
