#include <iostream>

 #include <cmath>

 using namespace std;

 const int maxn = ;

 bool dp[maxn][maxn];

 int a[maxn];

 double area(double a, double b, double c) {

     double p = (a+b+c)/;

     return sqrt(p*(p-a)*(p-b)*(p-c));

 }

 bool is_ok(int a, int b, int c) {

     if (a+b <= c || a+c <= b || b+c <= a)

         return false;

     return true;

 }

 int main() {

     int n; cin >> n;

     int sum = ;

     for (int i = ; i < n; i++) {

         cin >> a[i];

         sum += a[i];

     }

     dp[][] = true;

     for (int i = ; i < n; i++) {

         for (int k = ; k >= ; k--) {

             for (int j = k; j >= ; j--) {

                 if (k-a[i] >=  && dp[k-a[i]][j])

                     dp[k][j] = true;

                 if (j-a[i] >=  && dp[k][j-a[i]])

                     dp[k][j] = true;

             }

         }

     }

     double ans = ;

     for (int i = ; i <= ; i++) {

         for (int j = ; j <= i; j++) {

             if (dp[i][j] && is_ok(i,j,sum-i-j))

                 ans = max(ans,*area(i,j,sum-i-j));

         }

     }

     if (ans == ) cout << - << endl;

     else cout << (int)ans << endl;

     return ;

 }