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#include <bits/stdc++.h>
    using namespace std;
    #define ll long long
    #define st first
    #define nd second
    #define pii pair<int,int>
    #define pb push_back
    #define pp pop_back
    #define si size
    #define int ll
    #define V vector
;
#define cerr if(0) cerr

signed main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int n,k,sum=0;
    cin>>n>>k;
    vector<int> v(n);
    for(int i=0;i<n;i++)cin>>v[i];
    for(int j=0;j<n;j++){
        for(int i=0;i<n-1;i++){
            if(v[i]<v[i+1]){
                if(v[i+1]-k>v[i]){
                    sum+=v[i+1]-v[i]-k;
                    v[i]=v[i+1]-k;
                }
            }
            else{
                if(v[i]-k>v[i+1]){
                    sum+=v[i]-v[i+1]-k;
                    v[i+1]=v[i]-k;
                }
            }
        }
    }
    cout<<sum<<'\n';
}