#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
void solve()
{
    ll k=0,n=0,ans=0; vector<pair<ll,ll>> A,B; vector<ll> T;
    cin>>n>>k;
    for(int i=0; i<n; ++i){ll KWA; cin>>KWA; A.push_back({KWA,i}); T.push_back(KWA);}
    for(int i=0; i<n; ++i)
    {
        ll mx=-1,dx=-1;
        for(int j=0; j<n; ++j)
        {
            if(A[j].second==-1)continue;
            if(A[j].first>mx){mx=A[j].first; dx=A[j].second;}
        }
        A[dx].second=-1;
        if(dx!=0 and A[dx].first-A[dx-1].first>k){ans+=A[dx].first-k-A[dx-1].first; A[dx-1].first+=A[dx].first-k-A[dx-1].first;}
        if(dx!=n-1 and A[dx].first-A[dx+1].first>k){ans+=A[dx].first-k-A[dx+1].first; A[dx+1].first+=A[dx].first-k-A[dx+1].first;}
    }
    cout<<ans;
}
int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int MAKUMBA=1;
    //cin>>MAKUMBA;
    for(int KOKOJAMBO=0; KOKOJAMBO<MAKUMBA; ++KOKOJAMBO){solve();}
    return 0;
}