#include<iostream>
#include<string>
#include<cstdio>
#include<vector>
#include<cmath>
#include<algorithm>
#include<functional>
#include<iomanip>
#include<queue>
#include<ciso646>
#include<random>
#include<map>
#include<set>
#include<complex>
#include<bitset>
#include<stack>
#include<unordered_map>
using namespace std;
typedef long long ll;
typedef unsigned int ui;
const ll mod = (ll)(1e+9) + 7;
const ll INF = (ll)1000000007 * 1000000007;
typedef pair<int, int> P;
#define stop char nyaa;cin>>nyaa;
#define rep(i,n) for(int i=0;i<n;i++)
#define per(i,n) for(int i=n-1;i>=0;i--)
#define Rep(i,sta,n) for(int i=sta;i<n;i++)
#define rep1(i,n) for(int i=1;i<=n;i++)
#define per1(i,n) for(int i=n;i>=1;i--)
#define Rep1(i,sta,n) for(int i=sta;i<=n;i++)
typedef long double ld;
typedef complex<ld> Point;
const ld eps = 1e-8;
const ld pi = acos(-1.0);
typedef pair<ll, ll> LP;
typedef pair<ld, ld> LDP;
bool used[100], sused[100];
int n;
ld d[100]; int p[100];
int main(){
	cout << fixed << setprecision(1);
	cin >> n;
	ld out = 0;
	rep(i, n) {
		cin >> d[i] >> p[i]; p[i]--;
		out += d[i];
	}
	rep(i, n) {
		if (used[i])continue;
		fill(sused, sused + n,false);
		int cur = i; sused[i] = true;
		vector<int> v; v.push_back(i);
		while (true) {
			cur = p[cur];
			if (used[cur]) {
				break;
			}
			else if (sused[cur]) {
				int le = 0;
				rep(j, (int)v.size()) {
					if (v[j] == cur)le = j;
				}
				ld mi = 1000;
				Rep(j, le, v.size()) {
					mi = min(mi, d[v[j]]);
				}
				out += mi;
				break;
			}
			sused[cur] = true;
			v.push_back(cur);
		}
		rep(j, (int)v.size()) {
			used[v[j]] = true;
		}
	}
	cout << out / 2.0 << endl;
	return 0;
}