package main

import (
	"fmt"
	"math"
)

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

	cnt := 0
	for i := 0; i < n; i++ {
		_, _ = fmt.Scan(&c, &d)
		cnt = (cnt + int(math.Ceil(float64(c)/2))*d) % 10000000007
	}
	fmt.Println(cnt)
}