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

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

    int n, k;
    cin >> n >> k;
    vector<int> A(n);
    for (auto &a : A) {
        cin >> a;
    }

    priority_queue<pair<int, int>> Q;
    for (auto [i, a] : views::enumerate(A)) {
        Q.emplace(a, i);
    }

    vector<bool> vis(n);
    int64_t ans = 0;
    while (Q.size()) {
        auto [a, i] = Q.top();
        Q.pop();

        if (vis[i]) { continue; }
        vis[i] = true;

        for (auto j : {i - 1, i + 1}) {
            if (0 <= j && j < n && A[i] - A[j] > k) {
                ans += (A[i] - k) - A[j];
                A[j] = A[i] - k;
                Q.emplace(A[j], j);
            }
        }
    }
    cout << ans << '\n';
    return 0;
}