#include <bits/stdc++.h>
using namespace std;
long double area(long double a, long double b, long double c) {
  long double s = (a + b + c) / 2.0;
  return sqrt(s * (s - a) * (s - b) * (s - c));
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int i, j;
  long double l[9], a = 0;
  for (i = 0; i < 6; i++) cin >> l[i];
  for (i = 0, j = 6; i < 6; i += 2, j++) {
    l[j] =
        sqrt(((l[i]) * (l[i])) + ((l[i + 1]) * (l[i + 1])) + l[i] * l[i + 1]);
    a += area(l[i], l[i + 1], l[j]);
  }
  a += area(l[6], l[7], l[8]);
  int temp = (4.0 * a) / (long double)sqrt(3);
  cout << temp << '\n';
  return 0;
}
