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#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
#define st first
#define nd second

void solve() {
    int n, k; cin >> n >> k;
    vector<int> a(n);
    for (int i = 0; i < n; i++) cin >> a[i];
    ll ans = 0;
    for (int i = 1; i < n; i++) {
        int x = max(a[i], a[i-1]-k);
        ans += x - a[i];
        a[i] = x;
        for (int j = i-1; j >= 0; j--) {
            x = max(a[j], a[j+1]-k);
            ans += x-a[j];
            a[j] = x;
        }
    }
    cout << ans << '\n';
}


int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    int t = 1;
    // cin >> t;
    while (t--) {
        solve();
    }
}