# your code goes here
x=input('')
max=0
y=''
for i in x:
if(x.count(i)>max):
max=x.count(i)
y=i
print(y)
IyB5b3VyIGNvZGUgZ29lcyBoZXJlCng9aW5wdXQoJycpCm1heD0wCnk9JycKZm9yIGkgaW4geDoKCWlmKHguY291bnQoaSk+bWF4KToKCQltYXg9eC5jb3VudChpKQoJCXk9aQpwcmludCh5KQoJCQoJCQ==