Did a little digging and found the Counter.most_common(n) method, which returns the list you need to iterate print(*) through. Sorted the string beforehand because .most_common(n) will sort by order of elements encountered.

from collections import Counter


if __name__ == '__main__':
    s = sorted(input())
    s_count = Counter(s)
    [print(*entry) for entry in s_count.most_common(3)]