## Problem J. Jokers ≡

• problems
 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

0.069s 0.010s 13