# -*- coding: utf-8 -*-


N = int(input())
mod = 10**9 + 7
desks_list = [tuple(map(int, input().split())) for i in range(N)]
students = 0
for desk in desks_list:
    students += (desk[0] + 1) // 2 * desk[1]
    students %= mod
print(students)