TreeMap

import java.io.*;
import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        StreamTokenizer st
            = new StreamTokenizer(new BufferedReader(new InputStreamReader(System.in)));
        PrintWriter pw = new PrintWriter(System.out);

        st.nextToken();
        int n = (int) st.nval;

        TreeMap<Integer, Integer> map = new TreeMap<>();
        for (int i = 0; i < n; i++) {
            st.nextToken();
            int index = (int) st.nval;
            st.nextToken();
            int value = (int) st.nval;
            map.put(index, value + map.getOrDefault(index, 0));
        }
        for (Map.Entry<Integer, Integer> entry : map.entrySet()) {
            pw.printf("%d %d\n", entry.getKey(), entry.getValue());
        }

        pw.flush();
        pw.close();
    }
}