loop do
    n, m, k = gets.split.map(&:to_i)
    break if n == 0
    h = {0 => 1}
    n.times do
        h2 = Hash.new(0)
        (1..m).each do |x|
            h.each do |s, c|
                h2[s + x] += c
            end
        end
        h = h2
    end
    e = 0
    h.each do |s, c|
        e += [s - k, 1].max * c
    end
    p e.to_f / m ** n
end