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#include<bits/stdc++.h>
#define VAR(i,n) __typeof(n) i = (n)
#define loop(i,j,s) for(int i=j;i<s;i++)
#define loopback(i,j,s) for(int i=j;i>=s;i--)
#define foreach(i,c) for(VAR(i,(c).begin());i!=(c).end();i++)
#define pln( x ) cout << x << "\n"
#define ps( x ) cout << x << " "
#define entr cout << "\n"
#define pcnt(i) __builtin_popcount(i)
#define ll long long
#define pb push_back
#define mp make_pair
#define ff first
#define ss second
#define SIZE(c) (c).size()
#define ALL(c) (c).begin(), (c).end()
using namespace std;
typedef vector<int> VI;
typedef pair<int, int> PII;
typedef vector<vector<int> > VVI;
const int INFTY=20000000;
const int MAX=1100;
const int MOD=10000000;

void coutTab(int* tab,int n){
	loop(i,0,n){
		cout<<tab[i]<<" ";
	}
	cout<<"\n";
}

template<class T> void coutVec(vector<T> tab){
	for(T t : tab){
		cout<<t<<" ";
	}
	cout<<"\n";
}
//------------------------------------------
ll n,k;
ll a[MAX];

int main(){
	ios_base::sync_with_stdio(0);
    cin>>n>>k;
    for(int i=0;i<n;i++) cin>>a[i];

    priority_queue<pair<ll,int>> pq;
    loop(i,0,n) pq.push({a[i], i});

    vector<ll> b(n,-1);
    ll res=0;
    while(!pq.empty()) {
        auto [h, i] = pq.top(); pq.pop();
        if(b[i] != -1) continue;
        b[i] = h;
        if(h > a[i]) res += h - a[i];
        ll nh = h - k;
        if(nh <= 0) continue;
        if(i-1 >= 0 && b[i-1] == -1) pq.push({nh, i-1});
        if(i+1 < n && b[i+1] == -1) pq.push({nh, i+1});
    }
    pln(res);
}