Is better solution using Counter (as i learnt from other posting), anyway here is my solution.

from itertools import groupby

if name == 'main':

s = sorted(list(input()))

cap= [(k, len(list(g))) for k, g in groupby(s) ]

print (cap)
res = sorted(cap, reverse=True, key=lambda qty: qty[1])

for x in range(3):
print(res[x][0],res[x][1] )