n = int(input().strip())

# 使用字典存储每个索引对应的数值总和
index_sum = {}

for _ in range(n):
    x,y = map(int,input().split(" "))
    if x in index_sum:
        index_sum[x] += y
    else:
        index_sum[x] = y

sorted_index = sorted(index_sum.keys())

for index in sorted_index:
    print(f"{index} {index_sum[index]}")