package main

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


func main() {
	n := nextInt()
	var p[2000] float64
	var q[2000] float64
	for i := 0; i < n; i++ {
		p[i] = float64(nextInt())
		q[i] = float64(nextInt())
	}

	ans := 0.0
	for t := 0; t < 50000; t++ {
		best := -1
		bestp := -1.0
		for i := 0; i < n; i++ {
			findp := p[i] * q[i]
			if (findp > bestp) {
				bestp = findp
				best = i
			}
		}
		ans += p[best] * (q[best] / 100.0) * (float64(t) + 1.0)
		p[best] *= (100 - q[best]) / 100
	}
	fmt.Println(ans / 1000)
}


var s = bufio.NewScanner(os.Stdin)

func next() string {
	s.Split(bufio.ScanWords)
	s.Scan()
	return s.Text()
}
func nextLine() string {
	s.Split(bufio.ScanLines)
	s.Scan()
	return s.Text()
}

func nextInt() int {
	i, e := strconv.Atoi(next())
	if e != nil {
		panic(e)
	}
	return i
}
func nextLong() int64 {
	i, e := strconv.ParseInt(next(), 10, 64)
	if e != nil {
		panic(e)
	}
	return i
}