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#include <bits/stdc++.h>

using namespace std;

long long solve () {
    long long n, k;
    cin >> n >> k;
    vector<long long> a(n);
    for (long long i = 0; i < n; i++) {
        cin >> a[i];
    }

    vector<long long> pokrycie = a;
    for (long long i = 0; i < n; i++) {
        // Left:
        long long cur = a[i] - k;
        for (long long j = i + 1; j < n; j++) {
            pokrycie[j] = max(pokrycie[j], cur);
            cur -= k;
        }

        // Right:
        cur = a[i] - k;
        for (long long j = i - 1; j >= 0; j--) {
            pokrycie[j] = max(pokrycie[j], cur);
            cur -= k;
        }
    }

    long long ans = 0;
    for (long long i = 0; i < n; i++) {
        ans += pokrycie[i] - a[i];
    }

    return ans;
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

    cout << solve() << endl;
    return 0;
}