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#include<bits/stdc++.h>
using namespace std;
using ll = long long;
int main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int n, k;
    cin >> n >> k;
    vector<int>V(n);
    for(int i = 0; i < n; i++){
        int a;
        cin >> a;
        V[i] = a;
    }
    ll w = 0;
    vector<int>byl(n+99);
    for(int ep = 0; ep < 5*n+99;ep++){
        pair<int,int>maks = {0,0};
        for(int i = 0; i < n; i++){
            if(byl[i] < 3)
            maks = max(maks, make_pair(V[i],i));
        }
        int i = maks.second;
        byl[i]++;
        for(auto j : {i-1,i+1}){
            if(j < 0 || j >= n)continue;
            if(V[j] < V[i] - k){
                // cout << i << ", " << j << '\n';
                // cout << V[i] - k << " > " << V[j] << endl;
                w += V[i] - k - V[j];
                V[j] = V[i] - k;
            }
        }
    }
    cout << w << '\n';

}