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#include <bits/stdc++.h>
using namespace std;
int a, b;


int main() {
    ios::sync_with_stdio(0); cin.tie(0);
    cin >> a >> b;
    vector<int> nk, ok;
    for(int i = 0;i < a; i++) {
        int x; cin >> x;
        nk.push_back(x);
        ok.push_back(x);
    }
    for(int i = 1;i < a; i++) {
        ok[i] = max(ok[i], - b + ok[i - 1]);
    }
    for(int i = a - 2; i >= 0; i--) {
        ok[i] = max(ok[i], - b + ok[i + 1]);
    }
    int suma = 0;
    for(int i = 0;i < a; i++) {
        suma += ok[i] - nk[i];
    }
    cout << suma << endl;
    return 0;
}