n=int(input())
data = [list(map(int,input().split())) for i in range(n)]
sum=0

for i in range(n):
  if data[i][0]%2==0:
    data[i][0]/=2
  else:
    data[i][0]=int(data[i][0]/2)+1

  sum+=int(data[i][0]*data[i][1])

sum%(10**9+7)
print(sum)