import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {

static int[] w;
	static int[] p;
	static int[] val;
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		w = new int[n];
		p = new int[n];
		val = new int[n];
		int dd[] = new int[n];
		for (int i =0; i < n; i++) {
			dd[i] = 0;
			val[i] = 0;
		}

		for (int i = 0 ; i < n; i++) {
			w[i] = sc.nextInt()-1;
			p[i] = sc.nextInt();
			val[w[i]] ++;
		}
		boolean stop = false;
		while (!stop) {
			stop = true;
			for (int i =0 ; i < n; i++) {
				if (dd[i] == 0 && val[i] == 0) {
					stop = false;
					while (true) {
						dd[i] = 1;
						int j = w[i];
						if (dd[j] == 0) {
							val[j] --;
						}
						if (val[j] != 0) {
							break;
						}
						i = j;
					}
				}
			}
		}
		int count = 0;
		double result = 0;
		for (int i = 0 ; i < n ; i ++) {
			if (dd[i] == 0) {
				count ++;
				double pro = 1;
				while (true) {
					if (dd[i] != 0) {
						break;
					}
					if (w[i] == i) {
						break;
					}
					dd[i] = count;
					pro = pro * p[i] / 100;
					i = w[i];
				}
				result += pro;
			}
		}
		String str = String.format("%.2f", result);
		System.out.println(str);
	}
}