#include<bits/stdc++.h>
using namespace std;
#define pb push_back
#define mp make_pair
#define ft first
#define sd second
#define mem(a,v) memset(a,v,sizeof(a))
typedef long long int ll;
typedef pair<int, int> PII;

bool visited[100100];
bool visited1[100100];
int adj[100100];
double prob[100100];
double ans;
int par[100100];

void dfs(int u, int p)
{
    par[u] = p;
    if(visited[u]){
        visited1[u] = true;
        int u1  = u;
        double pr = 1.0;
        while(true){
            pr *= prob[par[u1]];
            u1 = par[u1];
            if(u == u1)
                break;
        }
        ans += pr;
        return;
    }
    visited[u] = true;
    if(!visited1[adj[u]])
        dfs(adj[u], u);
    visited1[u] = true;
}

int main()
{
    int n;
    cin>>n;
    for(int i=1; i<=n; i++){
        int x;
        double p;
        scanf("%d", &x);
        cin>>p;
        adj[i] = x;
        prob[i] = p/100.0;
    }
    for(int i=1; i<=n; i++){
        if(!visited[i]){
            dfs(i, -1);
        }
    }
    printf("%.2lf\n", ans);
	return 0;
}