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#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
#define rep(a,b) for(int a = 0; a < (b); ++a)
#define all(t) t.begin(), t.end()
#define pb push_back
#define fi first
#define se second
#define each(a,x) for(auto &a:x)
#define vi vector<int>
#define vll vector<ll>
#define vull vector<ull>
#define pi pair<int,int>
#define pll pair<ll,ll>
#define nl '\n'
#pragma GCC optimize ("O3")
#pragma GCC optimize ("unroll-loops")
#pragma GCC target("avx2")
#pragma GCC target("bmi")
#pragma GCC target("bmi2")
#pragma GCC target("lzcnt")
#pragma GCC target("popcnt")
const int N = 5e5+1234,INF = 2e9+1234,mod = 1e9+7;
const ll INF_L = (ll)2e18+1234;
void solve()
{
    int n,k;cin>>n>>k;vector<int>A(n),B(n);
    rep(i,n) cin>>A[i],B[i]=A[i];
    int ans=0;vector<bool> uz(n);
    rep(i,n)
    {
        int mx=-1;
        rep(j,n) if(!uz[j] and (mx == -1 or A[j]>A[mx])) mx=j;
        uz[mx]=1;
        if(mx-1>=0)A[mx-1]=max(A[mx-1],A[mx]-k);
        if(mx+1<n)A[mx+1]=max(A[mx+1],A[mx]-k);
    }
    rep(i,n) ans+=A[i]-B[i];
    cout << ans << nl;
}
int main()
{ 
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    int T=1;
    //cin >> T;
    while(T--) solve();
    return 0;
}