#!/usr/bin/env python3
# %%
import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines


# %%
import numpy as np
F, N, K = map(int, read().split())


# %%
x = np.arange(N + 1).astype(np.float64)
x[0] = 1
fact = np.multiply.accumulate(x)
comb = fact[N] / fact / fact[::-1]


# %%
P = [sum(comb[i] * (F - x) ** i * x ** (N - i) for i in range(K)) for x in range(F + 1)]
answer = F + 1 - sum(P) / P[-1]
print(answer)