#include <bits/stdc++.h>
using namespace std;
int n,t,x,maxn,last,lada;
int main()
{
    cin >> n >> t;
    cin >> x;
    last = x;
    lada = x + t - 1;
    maxn = t;
    for(int i = 2;i <= n;i++)
    {
        cin >> x;
        if(lada + 1 >= x)
        {
            lada += t - (lada - x + 1);
        }
        else
        {
            maxn += lada - last + 1;
            last = x;
            lada = x + t - 1;
        }
    }
    cout << maxn;
    return 0;
}

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