592 B | 592 chars
import sys
from math import sqrt, pi, sin, factorial, ceil, floor
from decimal import Decimal
BLANK = " "
#inp = input
inp = lambda : sys.stdin.readline()[:-1].strip()
mii = lambda x = BLANK : [*map(int,inp().split(x))]
mfi = lambda x = BLANK : [*map(float,inp().split(x))]
ii = lambda : int(inp())
fi = lambda : float(inp())
p = print
def solve():
s = input()
d = {}
for i in s:
d[i] = d.get(i, 0) + 1
d = sorted(d.items(), key = lambda t:(-t[1], t[0]))
for k, v in d:
print(end=k * v)
if __name__ == "__main__":
tc = 1
for t in range(1, tc+1):
ret = solve()