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#include<bits/stdc++.h>

using namespace std;

const int MAX = 500005;

int n, k;

vector <int> V;

int T[MAX];

long long wyn = 0;

bool f(){
    int maks=-1;
    int id=-1;
    for (int i=1; i<=n; i++){
        if (!T[i] && maks < V[i]){
            id = i;
            maks = V[i];
        }
    }
    if (id == -1) return 0;
    if (id > 1){
        if (V[id-1] < maks-k){
            wyn += maks-k - (V[id-1]);
            V[id-1] = maks-k;
        }
    }
    if (id < n){
        if (V[id+1] < maks-k){
            wyn += maks-k - (V[id+1]);
            V[id+1] = maks-k;
        }
    }
    T[id] = 1;
    return 1;
}

int main(){
    ios::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);

    cin >> n >> k;

    priority_queue <pair<int, int>> Q;

    V.push_back(0);

    int x;

    int r=1;

    for (int i=1; i<=n; i++){
        cin >> x;
        V.push_back(x);
        Q.push({x, i});
    }

    while (true){
        bool c = f();
        if (c == 0){
            cout << wyn << "\n";
            return 0;
        }
    }

    return 0;
}