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Competitions

# 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, f100). 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.

Time limit 1 second
Memory limit 128 MiB
Input example #1
3 4 4 2 5

Output example #1
9.7997

Source SFE-2010 Variant 26