#include<bits/stdc++.h>
using namespace std;
int a[200001];


int main()
{
    int n,t;
    cin>>n>>t;

    int happyday=0;
    for(int i=1;i<=n;++i)
        cin>>a[i];

    for(int i=1;i<n;++i)
    {
        if(a[i+1]-a[i]>=t)
            happyday+=t;


        else
            happyday+=a[i+1]-a[i];
    }


    cout<<happyday+t-1<<endl;

    return 0;
}

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