N = int(input())
if N < 5:
    print(0.0)
else:
    # Calculate numerator
    numerator = N * (N-1) * (N-2) * (N-3) * (N-4)
    # Precomputed denominator: 99*98*97*96*95 = 8582777280
    denominator = 8582777280
    # Probability for one line
    prob = numerator / denominator
    # Expected total bingos (12 lines)
    expected = 12 * prob
    # Print with sufficient precision
    print("{0:.11f}".format(expected))