def f(n,m,k,h);n==0?h:f(n-1,m,k,(1..m).map{|x|h.map{|s,c|[s+x,c]}.to_h}.inject{|a,b|a.merge!(b){|_,u,v|u+v}});end
while(n,m,k=gets.split.map &:to_i;n>0);p f(n,m,k,{0=>1}).map{|s,c|[s-k,1].max*c}.inject(:+).to_f / m ** n;end