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#include "bits/stdc++.h"

#define all(v) (v).begin(), (v).end()
#define st first
#define nd second
#define printv(a) { for(auto u : a) cout<<u<<" "; cout<<"\n"; }
#define debug(x) cerr << #x << " = " << x << '\n';

using namespace std;
using ll = long long;
using pii = pair<int,int>;
using vi = vector<int>;
using si = set<int>;
using mii = map<int,int>;

int tab[1005];

int main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int n,k;
    cin>>n>>k;
    int wyn = 0;
    for(int i=0;i<n;i++){
        cin>>tab[i];
        if(i==0) continue;
        if(tab[i] < tab[i-1] - k){
            wyn += tab[i-1] - k - tab[i];
            tab[i] = tab[i-1] - k;
        }
    }
    for(int i=n-1;i>=0;i--){
        if(i==n-1) continue;
        if(tab[i] < tab[i+1] - k){
            wyn += tab[i+1] - k - tab[i];
            tab[i] = tab[i+1] - k;
        }
    }
    cout<<wyn<<endl;
    return 0;
}