fac = [1.0]*101
for i in range(1,101):
    fac[i] = fac[i-1]*i
a,n,k = map(int,input().split())
ans = p = 0.0
for x in range(1,a+1):
    q = 0.0
    for z in range(k):
        q += fac[n]/fac[z]/fac[n-z]*pow(x/a,n-z)*pow((a-x)/a,z)
    ans += x*(q-p)
    p = q
print(ans)