f, n, k = map(int, input().split())
fact = [1.0];
for i in range(1,200):
    fact.append(fact[i-1] * i)

ret = 0
for i in range(f):
    s = 0;
    for j in range(n):
        for h in range(n):
            if (j <= n - k and n - k <= n - h - 1):
                s += (fact[n] / fact[j] / fact[h] / fact[n-j-h]) * (i ** j) * ((f-i-1) ** h);
    ret += (i + 1) * s;

print(ret / (f ** n))