F, N, K = map(int, input().split())
FACTORIALS = [1]
for i in range(100):
    FACTORIALS.append(FACTORIALS[i] * (i + 1))
ans = 0
for x in range(1, F + 1):
    for i in range(K):
        for j in range(K - i, N - i + 1):
            k = N - i - j
            ans += x * ((F - x) ** i) * ((x - 1) ** k) * FACTORIALS[N] // (FACTORIALS[i] * FACTORIALS[j] * FACTORIALS[k])
print(ans / (F ** N))