#include <iostream>#include <cstdio>#include <cstring>#include <algorithm>#include <cmath>using namespace std;double area(int a,int b,int c){if (a < b+c && a > abs(b-c)){double p = (a+b+c)/2.0;return sqrt(p*(p-a)*(p-b)*(p-c));}return 0;}double solve(int a[]){int sum = 0;for (int i = 1; i <= 6; i++)sum += a[i];double ans = 0,tmp;for (int i = 1; i <= 6; i++)for (int j = i+1; j <= 6; j++)for (int k = j+1; k <= 6; k++){int x = 0,y = 0,z = 0;for (int l = i+1; l <= j; l++)x += a[l];for (int l = j+1; l <= k; l++)y += a[l];z = sum - x - y;ans = max(ans,area(x,y,z));}return ans;}int main(){int a[10],b[10];while (scanf("%d",&a[1]) != EOF){for (int i = 2; i <= 6; i++)scanf("%d",&a[i]);int c[10] = {0,1,2,3,4,5,6};double ans = 0,tmp;do{int flag = 0;for (int i = 1; i <= 6; i += 2)if (abs(c[i]-c[i+1]) != 1){flag = 1;break;}if (flag)continue;for (int i = 1; i <= 6; i++)b[i] = a[c[i]];tmp = solve(b);if (tmp > ans)ans = tmp;}while (next_permutation(c+1,c+7));printf("%.12lfn",ans);}return 0;}
