package net.ipipip0129.yukicoder.no146;

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);

        int cnt = scan.nextInt();

        long capacity = 0;

        for (int i = 0; i < cnt; i++) {
            int chair = scan.nextInt();
            int desk = scan.nextInt();

            capacity += Math.ceil((double) chair / 2) * desk;
        }

        System.out.println((int) (capacity % (Math.pow(10, 9) + 7)));
    }
}