import sequtils, strutils, math, algorithm

var
    n = readLine(stdin).parseInt
    c = newSeq[int](n)
    d = newSeq[int](n)
    res:int
for i in 0..<n:
    (c[i],d[i]) =  readLine(stdin).split.map(parseInt)

for i in 0..<n:
    var canSit = int(ceil(c[i] / 2))
    res += canSit * d[i]

echo res mod int(10e9 + 7)