def fibonacci(n):
    """
    Find the nth number in the Fibonacci series.  Example:
    
    >>>fibonacci(100)
    354224848179261915075

    Algorithm & Python source: Copyright (c) 2013 Nayuki Minase
    Fast doubling Fibonacci algorithm
    http://nayuki.eigenstate.org/page/fast-fibonacci-algorithms
    """
    if n < 0:
        raise ValueError("Negative arguments not implemented")
    return _fib(n)[0]

# Returns a tuple (F(n), F(n+1))
def _fib(n):
    if n == 0:
        return (0, 1)
    else:
        a, b = _fib(n // 2)
        c = a * (2 * b - a)
        d = b * b + a * a
        if n % 2 == 0:
            return (c, d)
        else:
            return (d, c + d)
nt = 12

print("Project Euler 138 Solution =", sum(fibonacci(6*n+3)/2 for n in range(1, nt+1)))