CF559A.Gerald's Hexagon

Gerald got a very curious hexagon for his birthday. The boy found out that all the angles of the hexagon are equal to . Then he measured the length of its sides, and found that each of them is equal to an integer number of centimeters. There the properties of the hexagon ended and Gerald decided to draw on it.

He painted a few lines, parallel to the sides of the hexagon. The lines split the hexagon into regular triangles with sides of 1 centimeter. Now Gerald wonders how many triangles he has got. But there were so many of them that Gerald lost the track of his counting. Help the boy count the triangles.

杰拉尔德生日时收到了一个非常特别的六边形。他发现这个六边形的所有内角都等于 。接着，他测量了各边的长度，发现每条边的长度均为整数厘米。至此，该六边形的性质就全部明确了，杰拉尔德决定在它上面作画。

他画了几条与六边形各边平行的直线，这些直线将六边形分割成了若干个边长为 1 厘米的正三角形。现在，杰拉尔德想知道他一共得到了多少个这样的三角形。但由于数量实在太多，杰拉尔德在计数过程中弄丢了进度。请你帮助这位男孩计算出三角形的总数。

The first and the single line of the input contains 6 space-separated integers _a_1, _a_2, _a_3, _a_4, _a_5 and _a_6 (1 ≤ a__i ≤ 1000) — the lengths of the sides of the hexagons in centimeters in the clockwise order. It is guaranteed that the hexagon with the indicated properties and the exactly such sides exists.

输入仅有一行，包含六个以空格分隔的整数 $a_1,\ a_2,\ a_3,\ a_4,\ a_5$ 和 $a_6$（$1 \le a_i \le 1000$），表示按顺时针顺序给出的六边形各边的长度（单位：厘米）。题目保证满足所述性质且边长恰好为给定值的六边形一定存在。

Print a single integer — the number of triangles with the sides of one 1 centimeter, into which the hexagon is split.

输出一个整数——该六边形被分割成的边长为 1 厘米的三角形的个数。

This is what Gerald's hexagon looks like in the first sample:

And that's what it looks like in the second sample:

第一个样例中杰拉尔德的六边形如下所示：

第二个样例中它如下所示：