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

#define ll long long
#define st first
#define nd second
#define ld long double

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int n, k;
    cin >> n >> k;
    vector<ll> a (n);
    for (int i = 0; i < n; i++) {
        cin >> a[i];
    }
    ll ans = 0;
    for (int i = 0; i < n; i++) {
        bool b = 0;
        for (int j = 0; j < n-1; j++) {
            if (abs(a[j]-a[j+1]) > k) {
                if (a[j+1] < a[j]) {
                    ans += a[j]-a[j+1]-k;
                    a[j+1] = a[j]-k;
                    b = 1;
                }
                else {
                    ans += a[j+1]-a[j]-k;
                    a[j] = a[j+1]-k;
                    b = 1;
                }
            }
        }
        if (!b) {
            break;
        }
    }
    cout << ans << '\n';
}