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#include<iostream>
#include<vector>
using namespace std;

int main() {
    int n, k;
    cin >> n >> k;
    vector<int> arr(n);
    for (int i = 0; i < n; i++) {
        cin >> arr[i];
    }
    int gravel = 0;
    for (int i = 0; i < n - 1; i++) {
        int diff = arr[i + 1] - arr[i];
        if (diff > k) {
            arr[i] += diff - k;
            gravel += diff - k;
        } else if (-diff > k) {
            arr[i + 1] += - diff - k;
            gravel += - diff - k;
        }
    }
    for (int i = n-1; i > 0; i--) {
        int diff = arr[i] - arr[i - 1];
        if (diff > k) {
            arr[i - 1] += diff - k;
            gravel += diff - k;
        } else if (-diff > k) {
            arr[i] += - diff - k;
            gravel += - diff - k;
        }
    }
    cout << gravel << endl;
    return 0;
}