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#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define f first
#define s second
ll N, K, ans;
int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);

cin >> N >> K;
    vector<int> v(N);
    for (int i=0; i<N; i++) cin >> v[i];

    for (int i=0; i<1000; i++) {
        if (i%2==0) {
            for (int j=1; j<N; j++) {
                if (v[j]>=v[j-1]) continue;
                ll z=abs(v[j]-v[j-1])-K;
                if (z<=0) continue;
                v[j]+=z;
                ans+=z;
            }
            continue;
        }

        for (int j=N-2; j>=0; j--) {
            if (v[j]>=v[j+1]) continue;
            ll z=abs(v[j]-v[j+1])-K;
            if (z<=0) continue;
            v[j]+=z;
            ans+=z;
        }
    }
cout <<ans;
    return 0;
}