# -*- coding: utf-8 -*-
"""
No.146 試験監督（1）
https://yukicoder.me/problems/no/146

"""
import sys
# from sys import stdin
# input = stdin.readline


N = int(input())
numbers = []
for i in range(N):
    numbers.append([int(x) for x in input().split()])

ans = 0
for C, D in numbers:
    capacity = (C + 1) // 2
    ans += capacity * D
    ans %= (10**9+7)
print(ans)