from math import factorial
def comb(n,r):
    return factorial(n)/factorial(r)/factorial(n-r)

f,n,k=map(int,input().split())
ex=0
ls=[]
for i in range(f):
  ff=0
  p_i=(i+1)/f
  for j in range(n-k+1,n+1):
    ff+=comb(n,j)*(p_i**j)*((1-p_i)**(n-j))
  ls.append(ff)

p=[ls[i+1]-ls[i] for i in range(f-1)]
p.insert(0,ls[0])

for i in range(f):
  ex+=(i+1)*p[i]
print(ex)