#!/usr/bin/env python3
import math

N = int(input())
num = 0
mod = ((10 ** 9) + 7)
for i in range(N):
    C, D = [int(x) for x in input().split()]
    num += ((int(math.ceil(C / 2)) % mod) * D)
    num %= mod
num = num % mod
print(int(num))