#!/usr/bin/env python
#coding:utf8

def read():
    N = input()
    cdList = []
    for i in range(N):
        cdList.append(map(int, raw_input().split()))
    return cdList


def work(cdList):
    ans = 0
    for C, D in cdList:
        ans = ans + (C + 1) / 2 * D
    print ans % 1000000007


if __name__ == "__main__":
    work(read())