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#include <bits/stdc++.h>

using namespace std;

#define pii pair<int, int>

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

    vector<pii> values(n);
    vector<int> ogvals(n);
    for(int i = 0; i<n; i++){
        cin>>values[i].first;
        ogvals[i] = values[i].first;
        values[i].second = i;
    }

    sort(values.begin(), values.end());

    int out = 0;
    for(auto [val, pos] : values){
        int cpos = pos - 1;
        while(cpos >= 0){
            if(ogvals[cpos] >= ogvals[pos]) break;
            int tmp = ogvals[cpos + 1] - k;
            if(ogvals[cpos] < tmp){
                out += tmp - ogvals[cpos];
                ogvals[cpos] = max(ogvals[cpos], tmp);
            }
            cpos--;
        }

        cpos = pos + 1;
        while(cpos < n){
            if(ogvals[cpos] >= ogvals[pos]) break;
            int tmp = ogvals[cpos - 1] - k;
            if(ogvals[cpos] < tmp){
                out += tmp - ogvals[cpos];
                ogvals[cpos] = max(ogvals[cpos], tmp);
            }
            cpos++;
        }
    }

    cout<<out<<endl;
}