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#include<bits/stdc++.h>
#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/tree_policy.hpp>

using namespace std;
using namespace __gnu_pbds;

typedef long long ll;
typedef long double ld;

#define pb push_back
#define pii pair<int, int>
#define pll pair<ll, ll>
#define st first
#define nd second
#define ordered_set tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update>
#define debug false

const int MAXN = 1000 + 17;
ll a[MAXN];
ll b[MAXN];

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

    ll k;
    int n;
    cin >> n >> k;

    for (int i = 0; i < n; i ++) {
        cin >> a[i];
        b[i] = a[i];
    }

    ll wyn = 0;

    ll maks = a[0] - k;
    for (int i = 1; i < n; i ++) {
        b[i] = max(b[i], maks);
        maks = max(maks, a[i]) - k;
    }

    maks = a[n - 1] - k;
    for (int i = n - 2; i >= 0; i --) {
        b[i] = max(b[i], maks);
        maks = max(maks, a[i]) - k;
    }

    for (int i = 0; i < n; i ++) {
        wyn += (b[i] - a[i]);
    }

    cout << wyn << "\n";

    return 0;
}