num = int(input())
dic = {}
for i in range(num):
    line = input().split(' ')
    key = int(line[0])
    value = int(line[1])
    dic[key] = dic.get(key,0) + value
for key in sorted(dic):
    print(key,dic.get(key))

1.循环将输入的值存入字典中
2.按key将dic排序，依次取出