#include <iostream>
#include <fstream>
#include <vector>
#include <stack>
#include <queue>
#include <cstring>
#include <cmath>
#include <cstdlib>
#include <cstdio>
#include <algorithm>
#include <unordered_map>
#include <unordered_set>
#include <map>
#include <set>

using namespace std;

typedef long long ll;
typedef pair<int,int> PP;

/*
    freopen("input","r",stdin);
    freopen("output","w",stdout);
*/

int IN[100100];
int P[100100];
int V[100100];

int main() {
    ios::sync_with_stdio(false);
    int i,j,k,N,p;
    cin >> N;
    memset(IN,0,sizeof(IN));
    for (i = 1;i <= N;i++) {
    	cin >> V[i] >> P[i];
    	IN[V[i]]++;
    }
    queue<int> D;
    for (i = 1;i <= N;i++) {
    	if (IN[i] == 0) {
    		D.push(i);
    	} 
    }
    while (D.size() > 0) {
    	j = D.front();
    	D.pop();
    	IN[V[j]]--;
    	if (IN[V[j]] == 0) D.push(V[j]);
    	V[j] = 0;
    }
    double res = 0.0;
    for (i = 1;i <= N;i++) {
    	if (V[i] == 0) continue;
    	double ans = 1.0;
    	j = i;
    	while (V[j] != 0) {
    		ans *= double(P[j]) / 100.0;
    		k = V[j];
    		V[j] = 0;
    		j = k;
    	}
    	res += ans;
    }
    printf("%.2f\n", res);
    return 0;
}