#coding: utf-8
##yuki_146

n=int(raw_input())
s=[[0 for i in xrange(2)] for j in xrange(n)]
for i in range(n):
 l=[]
 l=map(int,raw_input().split())
 s[i][0]=l[0]
 s[i][1]=l[1]

res=0
for i in xrange(n):
 if s[i][0]%2==1:
  res+=((s[i][0]+1)/2)*s[i][1]
 elif s[i][0]%2==0:
  res+=(s[i][0]/2)*s[i][1]

print res%(10**9+7)