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

N = int(input())
num = 0
mod = ((10 ** 9) + 7)
desk = []
for line in sys.stdin:
    desk.append([int(x) for x in line.split()])

num = math.fmod(sum([math.ceil(c / 2) * d for c, d in desk]), mod)
print(int(num))