import re

s = 'How much wood would a woodchuck chuck if a woodchuck could chuck wood? Well? what do you think? Are you feeling well?'
l = re.split('[ ,?!.]', s.lower())

i, space = 0, []
while i < len(l):
    if l[i] == '':
        del l[i]
        i -= 1
    i += 1

duplicates = []
for i in range(len(l)):
    for j in range(len(l)):
        if j!=i and l[i]==l[j]:
            duplicates.append(l[j])

duplicates = set(duplicates)
temp = []
for item in duplicates:
    temp.append(item)
duplicates = temp

changed = True
while changed == True:
    changed = False
    for i in range(len(duplicates) - 1):
        if duplicates[i] > duplicates[i + 1]:
            duplicates[i], duplicates[i + 1] = duplicates[i + 1], duplicates[i]
            changed = True

for item in duplicates:
    print item