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#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
#define st first
#define nd second
#define pb push_back
#define pii pair<int,int>
#define pll pair<ll,ll>

const int maxn = 1003;

ll tab[maxn];

int main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    
    int n,k;
    cin>>n>>k;

    ll wyn = 0;
    for(int i=1;i<=n;i++){
        cin>>tab[i];
    }

    int x;
    for(int i=2;i<=n;i++){
        if(tab[i]+k < tab[i-1]){
            wyn += (tab[i-1]-k)-tab[i];
            tab[i] = tab[i-1]-k;
        }
        x = i;
        while(x > 1 && tab[x] > tab[x-1]+k){
            wyn += (tab[x]-k)-tab[x-1];
            tab[x-1] = tab[x]-k;
            x--;
        }
    }

    cout<<wyn<<"\n";
    
    return 0;
}