#!/usr/bin/python3
import sys

n, shirtpos, washs = [int(x) for x in sys.stdin.readline().split()]
expected = shirtpos * ((shirtpos-1)/n)**washs
for i in range(shirtpos, n+1):
    expected += (i+1)/2 * ((i/n)**washs - ((i-1)/n)**washs)
print(expected)