#include <bits/stdc++.h>

using i64 = long long;
using u64 = unsigned long long;
using u32 = unsigned;

using u128 = unsigned __int128;
using i128 = __int128;

int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    
    int n, k;
    std::cin >> n >> k;
    
    std::vector<int> a(n);
    for (int i = 0; i < n; i++) {
        std::cin >> a[i];
    }
    
    i64 ans = -std::accumulate(a.begin(), a.end(), 0LL);
    for (int i = 1; i < n; i++) {
        a[i] = std::max(a[i], a[i - 1] - k);
    }
    for (int i = n - 2; i >= 0; i--) {
        a[i] = std::max(a[i], a[i + 1] - k);
    }
    ans += std::accumulate(a.begin(), a.end(), 0LL);
    std::cout << ans << "\n";
    
    return 0;
}