package main

import (
	"bufio"
	"fmt"
	"math"
	"os"
	"strconv"
)

func main() {
	var n int
	_, _ = fmt.Scan(&n)

	var cnt int64
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	for i := 0; i < n; i++ {
		sc.Scan()
		c, _ := strconv.ParseInt(sc.Text(), 10, 64)
		sc.Scan()
		d, _ := strconv.ParseInt(sc.Text(), 10, 64)
		cnt = (cnt + int64(math.Ceil(float64(c)/2))*d) % 10000000007
	}
	fmt.Println(cnt)
}