def paraula_1(lpar):
   if len(lpar) == 1:
      parmax = lpar[0]
   else:
      par = paraula_1(lpar[1:])
      par1 = lpar[0]
      if par1.count('a') >= par.count('a'):
         parmax = par1
      else:
         parmax = par
   return parmax

def paraula_2(lpar, i=0):
    if i == len(lpar):
        parmax =  ''
    else:
        parmax1 = lpar[i]
        parmax2 = paraula_2(lpar, i+1)
        if parmax2.count('a') > parmax1.count('a'):
            parmax = parmax2
        else:
            parmax = parmax1
    return parmax

#tria la funció
paraula = paraula_1
#paraula = paraula_2