n = int(input())    # 输入键值对的个数
dic = {}            # 创建一个空字典
for i in range(0,n):
    key,value = map(int,input().split())
    dic[key] = dic.get(key,0) + value   # 累积key所对应的value

for each in sorted(dic):
    print(each,dic[each])