R

import operator

file = open('input.txt')
stack = []
s = ''

i = 0
for line in file:
    line = line.strip()
    if i == 0:
        i += 1
    else:
        stack.append(line.split())

file.close()

stack = sorted(stack, key = operator.itemgetter(0))

file = open('output.txt', 'w')
for i in stack:
    file.write(' '.join(i) + '\n')
    #print(i)
file.close()