#!/usr/bin/python3
#
# A program that reads a list of words from the standard input, with
# one word per line, and prints any one of the shortest words that
# appear least often.
#
import sys

D = {}

for w in sys.stdin:
    w = w.strip()
    if w in D:
        D[w] += 1
    else:
        D[w] = 1

min_v = None
min_len_w = None
for k,v in D.items():
    if min_v == None:
        min_v = v
        min_len_w = k
    elif v < min_v:
        min_v = v
        min_len_w = k
    elif v == min_v and len(k) < len(min_len_w):
        min_len_w = k

print(min_len_w)