#!/usr/bin/env python3
import math
import sys

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

num = num % mod
print(int(num))