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 = Integer.parseInt(scan.nextLine());

        long capacity = 0;

        for (int i = 0; i < cnt; i++) {
            String[] data = scan.nextLine().split(" ");

            capacity += Math.ceil((((double) Long.parseLong(data[0]))/2)) * Long.parseLong(data[1]) % (Math.pow(10, 9) + 7);
        }

        System.out.println(capacity);
    }
}