import sys



sys.setrecursionlimit(10 ** 7)

f_inf = float('inf')

mod = 10 ** 9 + 7





def resolve():

    n, m, d = list(map(int, input().split()))

    if d == 0:

        print(((m - 1) / n))

    else:

        print(((m - 1) * 2 * (n - d) / n ** 2))





if __name__ == '__main__':

    resolve()

import sys



sys.setrecursionlimit(10 ** 7)

input = sys.stdin.readline

f_inf = float('inf')

mod = 10 ** 9 + 7





def resolve():

    n, m, d = list(map(int, input().split()))

    print(((m - 1) / n if d == 0 else (m - 1) * (n - d) * 2 / pow(n, 2)))





if __name__ == '__main__':

    resolve()

import sys

sys.setrecursionlimit(10**7)
f_inf = float("inf")
mod = 10**9 + 7


def resolve():
    n, m, d = list(map(int, input().split()))
    if d == 0:
        print(((m - 1) / n))
    else:
        print(((m - 1) * 2 * (n - d) / n**2))


if __name__ == "__main__":
    resolve()

import sys

sys.setrecursionlimit(10**7)
input = sys.stdin.readline
f_inf = float("inf")
mod = 10**9 + 7


def resolve():
    n, m, d = list(map(int, input().split()))
    print(((m - 1) / n if d == 0 else (m - 1) * (n - d) * 2 / pow(n, 2)))


if __name__ == "__main__":
    resolve()

+input = sys.stdin.readline -    if d == 0: -        print(((m - 1) / n)) -    else: -        print(((m - 1) * 2 * (n - d) / n**2)) +    print(((m - 1) / n if d == 0 else (m - 1) * (n - d) * 2 / pow(n, 2)))