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#include<bits/stdc++.h>
#define ll long long
#define pb push_back
#define pll pair<ll,ll>
#define pii pair<int,int>
#define ld long double
using namespace std;
const int N = 1e3+1;
int h[N],n,k;


int main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    cin >> n >> k;
    for(int i = 1;i <= n;i++)cin >> h[i];
    ll total = 0;
    for(int i = 1;i < n;i++){
        if(h[i] - h[i+1] > k){
            total += h[i] - h[i+1] - k;
            h[i+1] += h[i] - h[i+1] - k;
        }
        if(h[i+1] - h[i] > k){
            total += h[i+1] - h[i] - k;
            h[i] += h[i+1] - h[i] - k;
        }
    }
    for(int i = n;i >= 2;i--){
        if(h[i] - h[i-1] > k){
            total += h[i] - h[i-1] - k;
            h[i-1] += h[i] - h[i-1] - k;
        }
        if(h[i-1] - h[i] > k){
            total += h[i-1] - h[i] - k;
            h[i] += h[i-1] - h[i] - k;
        }
    }
    cout << total;
}