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#include <cstdio>
#include <algorithm>
using namespace std;

int main() {
    int n;
    long long k;
    scanf("%d %lld", &n, &k);

    long long a[1000];
    for (int i = 0; i < n; i++)
        scanf("%lld", &a[i]);

    long long L[1000], R[1000];
    L[0] = a[0];
    for (int i = 1; i < n; i++)
        L[i] = max(L[i - 1], a[i] + k * i);

    R[n - 1] = a[n - 1] - k * (n - 1);
    for (int i = n - 2; i >= 0; i--)
        R[i] = max(R[i + 1], a[i] - k * i);

    long long ans = 0;
    for (int i = 0; i < n; i++) {
        long long b = max(L[i] - k * i, R[i] + k * i);
        ans += b - a[i];
    }

    printf("%lld\n", ans);
    return 0;
}