Competitions

# Functions

# Heron

The sides **a**, **b**, **c**, **d** and the diagonal **f** of a convex quadrilateral are given. Find the area of a quadrilateral, using the Heron’s formula that calculates the area of a triangle.

#### Input

In one line five real numbers are given: **a**, **b**, **c**, **d**, **f** (**0** < **a**, **b**, **c**, **d**, **f** ≤ **100**). They are the lengths of segments as shown in the picture.

#### Output

Print one number - the area of a quadrilateral calculated with accuracy of **4** digits after the decimal point.

Input example #1

3 4 4 2 5

Output example #1

9.7997