<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_ligands(pdb_id):
 """Return ligands of given PDB ID Parameters pdb_id : string A 4 character string giving a pdb entry of interest Returns ------- out : dict A dictionary containing a list of ligands associated with the entry Examples -------- {'id': '100D', 'ligandInfo': {'ligand': {'@chemicalID': 'SPM', '@molecularWeight': '202.34', '@structureId': '100D', '@type': 'non-polymer', 'InChI': 'InChI=1S/C10H26N4/c11-5-3-9-13-7-1-2-8-14-10-4-6-12/h13-14H,1-12H2', 'InChIKey': 'PFNFFQXMRSDOHW-UHFFFAOYSA-N', 'chemicalName': 'SPERMINE', 'formula': 'C10 H26 N4', 'smiles': 'C(CCNCCCN)CNCCCN'}}} """

    out = get_info(pdb_id, url_root = 'http://www.rcsb.org/pdb/rest/ligandInfo?structureId=')
    out = to_dict(out)
    return remove_at_sign(out['structureId'])