n, a, b = map(int, input().split())
print((4 * a * b * (b - a)) / (a ** 2 * n ** 2 - 2 * a ** 2 * n + a ** 2 - 2 * a * b * n ** 2 + 4 * a * b * n + 2 * a * b + b ** 2 * n ** 2 - 2 * b ** 2 * n + b ** 2))