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#include <iostream>
#include <vector>
#include <queue>
#include <utility>
#include <cmath>

using namespace std;

void input(int & n, int & k, vector<int> & heights) {
    cin >> n >> k;
    heights.resize(n);
    for(int i = 0; i < n; i++) {
        cin >> heights[i];
    }
}

int get_necessary_gravel(int const n, int const k, vector<int> & heights) {
    int result = 0;
    priority_queue<pair<int, int>> heights_queue;
    for(int i = 0; i < n; i++) {
        heights_queue.push({heights[i], i});
    }
    while(!heights_queue.empty()) {
        pair<int, int> cur_pair = heights_queue.top();
        heights_queue.pop();
        if(cur_pair.second > 0 && 
            (heights[cur_pair.second] - heights[cur_pair.second-1]) > k) {
                int needed_diff = heights[cur_pair.second] - heights[cur_pair.second-1] - k;
                result += needed_diff;
                heights[cur_pair.second-1] += needed_diff;
                heights_queue.push({heights[cur_pair.second-1], cur_pair.second-1});
        }
        if(cur_pair.second < n-1 && 
            (heights[cur_pair.second] - heights[cur_pair.second+1]) > k) {
                int needed_diff = heights[cur_pair.second] - heights[cur_pair.second+1] - k;
                result += needed_diff;
                heights[cur_pair.second+1] += needed_diff;
                heights_queue.push({heights[cur_pair.second+1], cur_pair.second+1});
        }
    }

    return result;
}

void solve() {
    int n, k;
    vector<int> heights;
    input(n, k, heights);

    cout << get_necessary_gravel(n, k, heights) << "\n";
}

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);

    solve();

    return 0;
}