#include <bits/stdc++.h>
#define f first
#define s second
#define ll long long
#define mp make_pair
#define pb push_back

using namespace std;

const int INF = int (1e9+7);
const int MAXN = int (5e5+7);

int n, x, y, a[200007], p[200007], color[200007];
double ans;

void dfs(int v) {
	color[v] = 1;
	if(!color[a[v]]) 
		dfs(a[v]);
	else if(color[a[v]] == 1) {
		double sum = (p[v] + 0.0) / 100;
		x = a[v];
		while(x != v) {
			sum *= (p[x] + 0.0) / 100;
			x = a[x];
		} 
		ans += sum;
	}
	color[v] = 2;
}

int main () {
	//freopen("input.txt", "r", stdin);
	//freopen("output.txt", "w", stdout);  

	cin >> n;
	for(int i = 1; i <= n; i ++) {
		scanf("%d%d", &a[i], &p[i]);
	}
	for(int i = 1; i <= n; i ++) {
		if(!color[i])
			dfs(i);
	}
	printf("%.2f", ans);
	return 0;
}