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Fast Fibonacci

By M.C. Pinto, UNILA BR Brazil

Timelimit: 1

Binet's formula is a way to calculate Fibonacci numbers.

Your task is, given a natural number n, to compute the value of Fibonacci(n) using the formula above.

Input

The input is a natural number n (0 < n ≤ 50).

Output

The output is the value of Fibonacci(n) with 1 decimal place using the given Binet's formula.

Input Samples Output Samples

1

1.0

2

1.0

3

2.0