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

#define int long long

int32_t main() {
    int n, k;
    std::cin >> n >> k;
    std::vector<int> vec(n);
    std::vector<bool> done(n, false);
    std::priority_queue<std::pair<int,int>> sorted;
    int out = 0;
    for (int i = 0; i < n; ++i) {
        std::cin >> vec[i];
        sorted.push({vec[i], i});
    }
    while (!sorted.empty()) {
        auto [v, i] = sorted.top();
        sorted.pop();
        if (!done[i]){
            done[i] = true;
            int max = vec[i];
            if (i > 0)
                max = std::max(max, vec[i - 1] - k);

            if (i < n - 1)
                max = std::max(max, vec[i + 1] - k);

            out += max - vec[i];
            vec[i] = max;

            if (i > 0)
                sorted.push({max - k, i - 1});

            if (i < n - 1)
                sorted.push({max - k, i + 1});
        }
    }

    std::cout << out << '\n';
}