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#include<bits/stdc++.h>
using namespace std;
long long xd[1009];
long long n,k,a;
long long fixLeft(int index)
{
long long res=0;
    while(index>1 && xd[index] - xd[index-1]>k)
    {
        res+=xd[index] - xd[index-1] - k;
        xd[index-1] += xd[index] - xd[index-1] - k;
        index--;
    }
    return res;
}
long long fixRight(int index)
{
    long long res=0;
    while(index<n && xd[index] - xd[index+1]>k)
    {
        res+=xd[index] - xd[index+1] - k;
        xd[index+1] +=  xd[index] - xd[index+1] - k;
        index++;
    }
    return res;
}
int main()
{
    ios_base::sync_with_stdio(0);
    cin>>n>>k;
    for(int i=1;i<=n;i++)
    cin>>xd[i];
    long long res=0;
    res+=fixRight(1);
    res+=fixLeft(n);
    for(int i=2;i<n;i++)
    {
        res+=fixLeft(i);
        res+=fixRight(i);
    }
    cout<<res<<endl;
    return 0;
}