#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;


int main() {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */   
    long long int n,i,j,s=0,m=0;
    cin>>n;
    long long int a[n+1],b[n+1],c[n+1];
    a[0]=0;
    b[0]=0;
    c[0]=0;
    for(i=1;i<=n;i++)
    {cin>>a[i];
    }

       for(i=1;i<=n;i++)
       {
           b[i]=b[i-1]+a[i];
           c[i]=c[i-1]+a[i]*a[i];
           s=b[i]*b[i]-c[i];
           if(s>m)
               m=s;
       }
    for(i=0;i<n;i++)
    {
        for(j=i+2;j<n;j++)
        {
            s=(b[j]-b[i])*(b[j]-b[i])-(c[j]-c[i]);
            if(s>m)
                m=s;
        }
    }
    cout<<m/2;
    
    return 0;
}