签到题没啥好说的
直接每一组的乘积之和即为结果

import java.math.*;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.io.StreamTokenizer;
import java.util.*;
public class Main {
    public static void main(String args[])throws IOException
    {
        StreamTokenizer in = new StreamTokenizer(new BufferedReader(new InputStreamReader(System.in)));
        PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));
        in.nextToken();
        int T = (int)in.nval;
        while(T-->0)
        {
             in.nextToken();
        int n = (int)in.nval;
            long ans=0;
            for(int i=0;i<n;i++)
            {
                in.nextToken();
        int x = (int)in.nval;
                in.nextToken();
        int y = (int)in.nval;
                ans+=x*y;
            }
        out.println(ans);
        out.flush();
        }

    }
                  }