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# Problem B

Hornrétt

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## Input

The input contains three integers $a$, $b$, and $c$, the side lengths of the triangle.

## Output

Print the area of the triangle if it’s possible to make a right angled triangle with side lengths $a$, $b$ and $c$, otherwise print $-1$.

## Scoring

Group |
Points |
Constraints |

1 |
50 |
$1 \leq a \leq b \leq c \leq 10^4$ |

2 |
50 |
$1 \leq a \leq b \leq c \leq 10^9$ |

Sample Input 1 | Sample Output 1 |
---|---|

3 4 5 |
6 |

Sample Input 2 | Sample Output 2 |
---|---|

4 6 7 |
-1 |