fac = [1.0]*101
for i in range(1,101):
    fac[i] = fac[i-1]*i
a,n,k = map(int,input().split())
print(a-sum(sum(fac[n]/fac[z]/fac[n-z]*pow(x/a,n-z)*pow((a-x)/a,z) for z in range(k)) for x in range(a)))