from functools import lru_cache

@lru_cache(maxsize=None)
def fact(n):
    return 1 if n == 0 else n * fact(n - 1)

f, n, k = map(int, input().split())

e = 0
for x in range(1, f + 1):
    p_l = (x - 1) / f
    p_c = 1 / f
    p_r = (f - x) / f
    
    p = 0
    for l in range(n - k + 1):
        for r in range(k):
            c = n - l - r
            p += p_l**l * p_c**c * p_r**r * fact(n) / (fact(l) * fact(c) * fact(r))
    
    e += p * x

print(e)