Accessing data in CSV

Question

The code is to separate the values of each state in different lists, so the variable 'o' changes all once the state acronym changes and tells which list the values will be. It works until the penultimate change but in the last it returns the error Keyerror: 5596. No problem in the file as I can access this line through separate prints and appends.

import pandas as pd
import matplotlib.pyplot as plt
dados=pd.read_csv('salarios.csv',sep=',')

tamanho=len(dados)
anos=[]
for i in range(27):
    anos.append([])
o=0

sigla=dados['Sigla']

for i in range(tamanho):
    if sigla[i]!=sigla[i+1]:
        print(sigla[i])
        o=o+1`