package main

import (
    "bufio"
    "fmt"
    "os"
    "sort"
    "strconv"
    "strings"
)

func main() {
    scanner := bufio.NewScanner(os.Stdin)

    for scanner.Scan() {
        mp := make(map[int]int, 500)
        input := scanner.Text()
        if len(input) == 0 {
            break
        }

        end, _ := strconv.Atoi(input) // str转int
        for i := 0; i < end; i++ {
            scanner.Scan()                        // 重新扫描
            arr := strings.Fields(scanner.Text()) // 字符串分隔
            k, _ := strconv.Atoi(arr[0])
            v, _ := strconv.Atoi(arr[1])

            if val, ok := mp[k]; ok { // 判断 map 键值对是否存在
                mp[k] = v + val
            } else {
                mp[k] = v
            }
        }

        keys := make([]int, 0, 500) // 提取 keys
        for key := range mp {
            keys = append(keys, key)
        }
        sort.Ints(keys) // 数组排序
        for _, item := range keys {
            fmt.Printf("%d %d\n", item, mp[item])
        }
    }

}