import core.bitop;
import std.algorithm;
import std.ascii;
import std.bigint;
import std.conv;
import std.functional;
import std.math;
import std.numeric;
import std.range;
import std.stdio;
import std.string;
import std.random;
import std.typecons;
import std.container;

alias sread = () => readln.chomp();
long bignum = 1_000_000_007;

T lread(T = long)()
{
    return readln.chomp.to!T();
}

T[] aryread(T = long)()
{
    return readln.split.to!(T[])();
}

void scan(TList...)(ref TList Args)
{
    auto line = readln.split();
    foreach (i, T; TList)
    {
        T val = line[i].to!(T);
        Args[i] = val;
    }
}

void main()
{
    long n, t;
    scan(n, t);
    auto l = aryread();
    long shower;
    foreach (i; 0 .. n)
    {
        if (i == 0)
            continue;

        if (l[i - 1] + t > l[i])
        {
            shower += l[i] - l[i - 1];
        }
        else
        {
            shower += t;
        }
    }
    shower += t;
    shower.writeln();
}
