Help on gr_make_io_signature

GNU Radio
1

Hi,
  I am writing a block to concatenated data from two input streams of
different length and i am using following I/O signatures

ACS_combine_vff::ACS_combine_vff(int len)
 : gr_sync_block(“ACS_combine_vff”,
       gr_make_io_signature(1,2, sizeof(float)*len),
       gr_make_io_signature(1,1, sizeof(float)2len))
  Â
{
   d_len=len;

}

suppose if i have first input stream of length 10 and second input
stream of length 5 , how should i modify the above I/O signature to make
sure output stream has length 15 .

thanks in advance
Raman