#include <bits/stdc++.h>

typedef long long ll;

using namespace std;

int main(){
    cin.tie(0)->sync_with_stdio(0);

    int n, k;

    cin >> n >> k;

    vector<int> tab(n+2);
    tab[0] = 1e9+7;
    tab[n+1] = 1e9+7;
    priority_queue<pair<int,int>> pq;

    for(int i = 1; i <= n; i++){
        cin >> tab[i];
        pq.push({tab[i], i});
    }

    int ans = 0;

    while(!pq.empty()){
        auto [x, i] = pq.top();
        pq.pop();
        if(x != tab[i])continue;
        if(tab[i-1] < tab[i] - k){
            ans += tab[i] - k - tab[i-1];
            tab[i-1] = tab[i] - k;
            pq.push({tab[i-1], i-1});
        }
        if(tab[i+1] < tab[i] - k){
            ans += tab[i] - k - tab[i+1];
            tab[i+1] = tab[i] - k;
            pq.push({tab[i+1], i+1});
        }
    }

    cout << ans << '\n';

    return 0;
}