#include<iostream>
#include<vector>
#include<algorithm>

void set(int& pile, int value, int& result)
{
    result += value - pile;
    pile = value;
}

void fix(int pos, std::vector<int>& tab, int k, int& result) {
    if (pos == 0 || tab[pos - 1] >= tab[pos] - k) {
        return;
    }
    set(tab[pos - 1], tab[pos] - k, result);
    fix(pos - 1, tab, k, result);
}

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

    int n, k;
    std::cin >> n >> k;

    std::vector<int> tab(n);
    for (int i = 0; i < n; ++i) {
        std::cin >> tab[i];
    }
    
    int result = 0;
    for (int phase = 0; phase < 2; ++phase) {
        for (int i = 0; i < n; ++i) {
            fix(i, tab, k, result);
        }
        std::reverse(tab.begin(), tab.end());
    }
    std::cout << result << '\n';
}