loop do
    n, m, k = gets.split.map(&:to_i)
    break if n == 0 && m == 0 && k == 0
    sum = 0
    dp = Array.new(n * m + 1, 0)
    dp[0] = 1.0
    n.times do
        dp2 = Array.new(n * m + 1, 0)
        dp.each_with_index do |d, i|
            next if d == 0
            1.upto(m) do |j|
                break if i + j > n * m
                dp2[i + j] += d / m.to_f
            end
            dp = dp2
        end
    end
    dp.each_with_index do |d,i|
        i -= k
        i = 1 if i < 1
        sum += d * i
    end
    puts sum
end