while (n, m, k = gets.split.map(&:to_i)).inject(:+) != 0 do
  answer = 0.0
  denominator = m**n
  dp = Array.new(n){Array.new(m*n + 1, 0)}
  dp[0][1, m] = Array.new(m, 1)
  for i in 1...n do
    for j in 1..m*n do
      for x in 1..m do
        break if j+x > m*n
        dp[i][j+x] += dp[i-1][j]
      end
    end
  end
  for i in 1..n*m do
    answer += [i - k, 1].max.to_f * dp[n - 1][i].to_f / denominator
  end
  p answer
end