10.py

string = ""
s = input()
while s != "ФИНИШ":
    string += s
    s = input()

string = string.lower().replace(" ", "")

d = {}

for i in string:
    if i in d:
        d[i] += 1
    else:
        d[i] = 1

maxl, s = 0, "я"
for i in d.keys():
    if d[i] > maxl:
        maxl = d[i]    
        s = i
    elif d[i] == maxl:
        if ord(i) < ord(s):
            s = i

print(s)