#coding: UTF-8

import sys
import re
import itertools
from math import log
from collections import deque

### defs ###


### main ###
N = int(sys.stdin.readline())
CD = []
for _ in range(N):
	c,d = map(int,sys.stdin.readline().split())
	CD.append((c,d))

ans=0
for cd in CD:
	ans = (ans + (cd[0]+1)//2 * cd[1]) % 1000000007
print(ans)