# Heron

Very easy

Execution time limit is 1 second

Runtime memory usage limit is 128 megabytes

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: $a,b,с,d,f(0<a,b,c,d,f≤100)$. They are the lengths of segments as shown in the picture.

## Output

Print the area of a quadrilateral with $4$ decimal digits.

## Examples

Input #1

Answer #1

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