var A,B,C,K,N:longint;

function CazuriFavorabile:longint;
 var aux,i:longint;
 begin
     CazuriFavorabile:=0;
     i:=A;
      while i<=B do
        begin
            aux:=i;
            while aux>0 do
              begin
                  if aux mod 10=C then
                    begin
                        inc(CazuriFavorabile);
                        aux:=aux div 10;
                         break
                    end else aux:=aux div 10;
              end;
            inc(i);
        end;

 end;




BEGIN
      assign(input,'cifre.in'); reset(input);
      assign(output,'cifre.out'); rewrite(output);
      readln(input,A,B,C,K);
      N:=CazuriFavorabile();
      write(output,N/((B-A)+1):5:4);
      close(input);
      close(output);
END.