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#include <iostream>
#include <vector>

using namespace std;

typedef long long ll;

int main() {
    ios_base::sync_with_stdio(false);

    ll n, k;
    cin >> n >> k;
    vector<ll> sizes(n);

    for (int i = 0; i < n; i++) {
        cin >> sizes[i];
    }

    ll sum = 0;
    for (int i = 1; i < n; i++) {
        const ll new_size = max(sizes[i], sizes[i - 1] - k);
        sum += abs(sizes[i] - new_size);
        sizes[i] = new_size;
    }

    for (int i = sizes.size() - 2; i >= 0; i--) {
        const ll new_size = max(sizes[i], sizes[i + 1] - k);
        sum += abs(sizes[i] - new_size);
        sizes[i] = new_size;
    }

    cout << sum << endl;

    return 0;
}