// Created by Abhishek Kumar
#include<bits/stdc++.h>
#define ll long long
#define MOD (ll)(1e9+7)
#define MAX (ll) (1e6+1)
#define C(x) cin>>x
#define CC(X,Y) cin>>x>>y
#define CCC(X,Y,Z) cin>>X>>Y>>Z
#define O(x) cout<<x
#define ENDL cout<<endl
#define loop(i,a,b) for(ll i = a; i<b;++i)
#define loops(i,a,b) for(ll i = a; i<=b; ++i)
#define pb(x) push_back(x)
#define pii pair<ll,ll>
#define vs vector<string>
#define li list<ll>
#define vs vector<string>
#define ls list<string>
#define pf(x) push_front(x)
#define ppb() pop_back()
#define ppf() pop_front()
#define vpi vector<pii>
#define mp(x,y) make_pair(x,y)
#define vi vector<ll>
#define finder(v,a) (find(v.begin(),v.end())!=v.end())
#define msvi map<string,vi>
#define msvs map<string,vs>
#define mii map<ll,ll>
#define msi map<string,ll>
#define isKey(map,key) (map.find(key) != map.end())
#define ff first
#define ss second
#define psi pair<ll,string>
#define pis pair<ll,string>
#define pivs pair<ll,vs>
#define si set<ll>
#define mspivs map<string,pivs>
using namespace std;

bool isPrime(ll n)
{
    if(n==2)
        return true;
    if(!(n%2))
        return false;
    for(ll i = 3; i<= sqrt(n); i+=2)
            if(!(n%i))
                return false;
    return true;
}

ll gcd(ll a, ll b)
{
    if(b==0)
        return a;
    return ((a>b)?gcd(b,a%b):gcd(a, b%a));
}

ll digitSum(ll n)
{
    ll sum = 0;
    while(n>0)
    {
        sum+=(n%10);
        n/=10;
    }
    return sum;
}

ll solve(int *a,int n)
{
    ll dp[n];
    dp[0] = 0;
    loop(i,1,n)
    {
        ll sum = a[i] + a[i-1];
        ll val = a[i]*a[i-1];
        ll ans = val;
        for(int j = i - 2; j >= 0; --j)
        {
            val += (a[j]*sum);
            ans = max(ans,val);
            sum += a[j];
        }
        dp[i] = ans;
    }
    return *max_element(dp+1,dp+n);
}

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
    int n;
    cin>>n;
    int a[n];
    loop(i,0,n)
        cin>>a[i];
    cout<<solve(a,n)<<endl;
    return 0;
}