#include<bits/stdc++.h>
using namespace std;
#define DB(x){if(DEBUG)cerr<<__LINE__<<" "<<#x<<" " <<x<<endl;}
#define REP(i,b)for(LL i=(0);i<(b);++i)
#define FOR(i,a,b)for(LL i=(a);i<=(b);++i)
#define FORD(i,a,b)for(LL i=(a);i>=(b);--i)
#define ALL(x) (x).begin(),(x).end()
template<typename X,typename Y>void MAX(X&a,Y b){a=(a>=b?a:b);}
template<typename X,typename Y>void MIN(X&a,Y b){a=(a<=b?a:b);}
typedef long long LL;typedef long double LD;
int DEBUG=0,MULTI=0,GCJ=0;
#define VV vector

struct solver_t;solver_t *solver;
struct solver_t {


  void solve() {
    int N ; cin >> N;
    VV<LL> A(N + 1);
    FOR (i, 1, N) cin >> A[i];
    LL sum = 0;

    VV<LL> SUM(N + 1);
    LL res = 0;

    FOR (i, 1, N) {
      LL tmp = 0;
      FORD (j, i - 1, 1) {
        SUM[j] += A[j] * A[i];
        tmp += SUM[j];
        MAX( res, tmp );
      }
    }

    DB(sum);
    cout << res << "\n";
  }
  void gen() {}
  void brute() {}
};

int main(int argc,char** argv){
  FOR(i,1,argc-1)for(int j=0;argv[i][j];j++)if(argv[i][j]=='.')freopen(argv[i],"r",stdin);
  FOR(i,1,argc-1)if(argv[i]==string("q"))DEBUG=1<<30;
  FOR(i,1,argc-1)if(argv[i]==string("gen")){(solver=new solver_t())->gen();exit(0);}
  FOR(i,1,argc-1)if(argv[i]==string("brute")){(solver=new solver_t())->brute();exit(0);}
  ios::sync_with_stdio(false),cin.tie(0);
  cout.setf(ios::fixed),cout.precision(10);int t;if(MULTI||GCJ)cin>>t;else t=1;
  FOR(i,1,t){if(DEBUG)cerr<<__LINE__<<" "<<i<<endl;if(GCJ)cout<<"Case #"<<i<<": ";
    solver = new solver_t();
    solver->solve();
  }return 0;
}