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

import math

N = int(input())
C = []
D = []
for i in range(N):
    c,d = map(int, input().split())
    C.append(c)
    D.append(d)

answer = 0
M = pow(10,9) + 7
for i in range(N):
    answer += (math.ceil(C[i]/2)) * D[i]
    answer %= M

print(answer)