#!/usr/bin/env python
import random
from letters import file2pairs
import sys

file = sys.argv[1]
prev_letter = sys.argv[2]
letters_dict = file2pairs(file)
prob = letters_dict[prev_letter]
p_value = prob.values()
support = 'abcdefghijklmnopqrstuvwxyz '
answer = random.choices(support,p_value)
print(answer[0])