Problem J. Jokers ≡

 Author: G. Grenkin Time limit: 1 sec Input file: input.txt Memory limit: 256 Mb Output file: output.txt

Statement

Once upon a time Marfa Gennadievna bought a pack of 54 playing cards containing two jokers. She put cards face down and chose N cards of them randomly (with uniform probability distribution).

Your program must calculate the probability that there will be at least one joker among chosen cards.

Input file format

Input file contains a single integer N.

Output file format

Output file must contain a single real number — required probability with at least 6 correct digits after decimal point.

2 ≤ N ≤ 54

Sample tests

No. Input file (input.txt) Output file (output.txt)
1
2
0.073375
2
10
0.338924

0.074s 0.008s 15