#coding=UTF-8

# 1  2  3  4  5  6
# 1  1  2  2  3  3
import math

N=int(input())
ans=0

for idx in range(0,N,1):
    mojir=input()
    hyo=mojir.split(" ")
    C=int(hyo[0])
    D=int(hyo[1])
    ans=(ans+math.ceil(C/2)*D)%(10**9+7)

print(ans)