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

public class A {
	public static void main(String[] args) throws IOException {

		// For STDIN, put two stars below.
		// For File In, put one star below.
		/**/
		Scanner sc = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
		/*/
		Scanner sc = new Scanner(new BufferedReader(new InputStreamReader(new FileInputStream("src/a.in"))));
		/**/
		
		int n = sc.nextInt();
		int[] cities = new int[n];
		int[] probs = new int[n];
		boolean[] visited = new boolean[n];
		double total = 0;
		for (int i = 0; i < n; i++) {
			cities[i] = sc.nextInt()-1;
			probs[i] = sc.nextInt();
		}
		
		for (int i = 0; i < n; i++) {
			int c = i;
			if (!visited[c]) {
				Set<Integer> tempVisited = new HashSet<Integer>();
				double d = 1;
				while (!visited[c] && !tempVisited.contains(c)) {
					tempVisited.add(c);
					d *= probs[c];
					d /= 100;
					c = cities[c];
				}
				if (c == i) {
					total += d;
					for (int city : tempVisited) {
						visited[city] = true;
					}
				}
			}
		}
		
		System.out.printf("%.2f", total);
	}
}