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#include<bits/stdc++.h>
using namespace std;

const int maxN = 1e3;
const int maxK = 1e6;

int n, k;
int arr[maxN+5];
int res;

int main()
{
    cin >> n >> k;
    for(int i = 1; i <= n; i++){
        cin >> arr[i];
    }
    for(int i = 2; i <= n; i++){
        if( arr[i-1]-arr[i] > k ){
            res += (arr[i-1]-k -arr[i]);
            arr[i] = arr[i-1]-k;
        }
    }
    for(int i = n-1; i >= 1; i--){
        if( arr[i+1]-arr[i] > k ){
            res += (arr[i+1]-k -arr[i]);
            arr[i] = arr[i+1]-k;
        }
    }
    cout << res << "\n";
    return 0;
}