def past_verb(s_verb):
    d = {'play': 'played',
         'stop': 'stopped',
         'go': 'gone',
         'put': 'put'}

    str = d.get(s_verb)

    if str is None:
        # y -> ied
        if s_verb[-1:] == 'y':
            str = s_verb[:-1] + 'ied'
        # e -> ed
        elif s_verb[-1:] == 'e':
            str = s_verb[:-1] + 'ed'
        # c -> ked
        elif s_verb[-1:] == 'c':
            str = s_verb + 'ked'
        else :
            str = s_verb + 'ed'

    return str


print(past_verb("play"))
print(past_verb("like"))
print(past_verb("try"))
print(past_verb("stop"))
print(past_verb("heat"))
print(past_verb("picnic"))
print(past_verb("go"))
print(past_verb("put"))