loop do
    n, m, k = gets.split.map(&:to_i)
    break if n == 0 && m == 0 && k == 0
    sum = 0
    count = 0
    (1..m).to_a.repeated_permutation(n).each do |a|
        s = a.inject(:+) - k
        s = 1 if s < 1
        sum += s
        count += 1
    end
    puts sum.to_f/count.to_f
end