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#include <bits/stdc++.h>
#define ll long long
using namespace std;

void solve(ll l, ll r, vector<ll>& v, vector<bool>& taken, ll &ans, ll k){
    if(l == r) return;

    ll maxi = -1, idx = 0;
    for(ll i=l; i<r; i++){
        if(taken[i]) continue;
        if(v[i] > maxi){
            maxi = v[i];
            idx = i;
        }
    }

    taken[idx] = 1;
    if(idx != 0 && idx-1 >= l && !taken[idx-1]){
        ll r = maxi - v[idx-1];
        if(r > k){
            r -= k;
            v[idx-1] += r;
            ans += r;
        }
    }

    if(idx != (ll)(v.size())-1LL && idx+1 < r && !taken[idx+1]){
        ll r = maxi - v[idx+1];
        if(r > k){
            r -= k;
            v[idx+1] += r;
            ans += r;
        }
    }

    solve(l, idx, v, taken, ans, k);
    solve(idx+1, r, v, taken, ans, k);
}
 
void solve(){
    ll n, k; cin>>n>>k;
    vector<ll> v(n, 0); for(auto &e: v) cin>>e;
    vector<bool> taken(n, 0);

    ll ans = 0;

    solve(0, n, v, taken, ans, k);

    cout<<ans<<'\n';
}
 
int main(){
    ios_base::sync_with_stdio(0);
    cout.tie(0); cin.tie(0);
 
    int sets=1; 
    //cin>>sets;
    while(sets--){
        solve();
    }
    return 0;
}