#include <iostream>
#include <iomanip>
#include <algorithm>
#include <vector>
#include <string>
#include <cmath>
#include <memory.h>
#include <sstream>
#include <stack>
#include <fstream>
#include <cstdio>
#include <unordered_map>
#include <map>
#include <list>
#include <stdlib.h>
#include <queue>
#include <set>
using namespace std;

int n;
int p[100001];
double pr[100001];

int col[100001];
double ex;
void dfs(int i)
{
	if (col[i] == 2) return;
	if (col[i] == 1)
	{
		int cur = i;
		double mul = 1;
		do
		{
			mul *= pr[cur];
			cur = p[cur];
		} while (cur != i);
		ex += mul;
		col[i] = 2;
		return;
	}
	col[i] = 1;
	dfs(p[i]);
	col[i] = 2;
}

int main()
{
	cin>>n;
	ex = 0;
	for(int i = 0; i < n; i++)
	{
		double x;
		cin>>p[i]>>x;
		p[i]--;
		pr[i] = x / 100.0;
	}
	memset(col, -1, sizeof(col));
	for (int i = 0; i < n; i++) {
		dfs(i);
	}
	cout<<fixed<<setprecision(2)<<ex<<endl;
}