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#include <iostream>
#include <climits>
#include <vector>

const int INF = INT_MAX;

void solve() {
    int n, k;
    std::cin >> n >> k;

    std::vector<int> a(n);
    for (auto& x : a) std::cin >> x;

    int sum = 0;

    for (int i = 0; i < n; i++) {
        if (i > 0 && a[i] < a[i-1] - k) {
            sum += a[i-1] - k - a[i];
            a[i] += a[i-1] - k - a[i];
        }
        if (i < n-1 && a[i] < a[i+1] - k) {
            sum += a[i+1] - k - a[i];
            a[i] += a[i+1] - k - a[i];

            for (int j = i-1; j >= 0; j--) {
                if (a[j] < a[j+1] - k) {
                    sum += a[j+1] - k - a[j];
                    a[j] += a[j+1] - k - a[j];
                }
                else break;
            }
        }
    }

    std::cout << sum << '\n';
}

int main() {
    std::ios_base::sync_with_stdio(false);
    std::cin.tie(nullptr);
    std::cout.tie(nullptr);

    solve();

    return 0;
}