In mature insulin, the C-peptide and the four basic residues have been excised and the B- and A-chains are connected covalently only by the two disulfide bonds between the B7-A7 and B19-A20 cysteines.
If this is required, one could use the server European Bioinformatics Institute.
Human insulin consists of 51 amino acids, divided into two chains, commonly labelled A and B, with 21 and 30 amino acids respectively.