# 20240910
n = int(input())
dic = {}
for i in range(n):
    k,v = map(int,input().split())
    if k not in dic:
        dic[k] = v
    else:
        dic[k] = dic.get(k,0) + v
ld = sorted(dic.items())

for k,v in ld:
    print(k,v)