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#include <bits/stdc++.h>
using namespace std;
using i64 = int64_t;
using u64 = uint64_t;

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    
    i64 n, k;
    cin >> n >> k;

    vector<i64> nums(n);
    i64 ans = 0;
    for (auto& i : nums) cin >> i;

    for (int i = 1; i < n; i++) {
        if (nums[i - 1] != -1 && nums[i - 1] > nums[i] + k) {
            i64 toAdd = nums[i - 1] - (nums[i] + k);
            ans += toAdd;
            nums[i] += toAdd;
        }
    }

    for (int i = n - 2; i >= 0; i--) {
        if (nums[i + 1] != -1 && nums[i + 1] > nums[i] + k) {
            i64 toAdd = nums[i + 1] - (nums[i] + k);
            ans += toAdd;
            nums[i] += toAdd;
        }
    }

    cout << ans << "\n";
    
}