package main

import "fmt"

// 10^9 + 7
const P = 1000000007

func main() {
	var N int
	fmt.Scan(&N)
	var res int64
	for i := 0; i < N; i++ {
		var C, D int64
		fmt.Scan(&C, &D)
		res += ((C/2 + C%2) % P) * (D % P)
		res %= P
	}
	fmt.Println(res)
}