Odd Occurrences

line = input().lower()
words = line.split(' ')

counts = {}
for word in words:
    if word in counts:
        counts[word] += 1
    else:
        counts[word] = 1
results = []
for key, value in counts.items():
    if value % 2 == 1:
        results.append(key)


print(", ".join(results))