/* preprocessor start */
#ifdef LOCAL
    #define _GLIBCXX_DEBUG  // gcc
    #define _LIBCPP_DEBUG 0 // clang
    #define __clock__
#else
    #pragma GCC optimize("Ofast")
    // #define _GLIBCXX_DEBUG
    // #define _LIBCPP_DEBUG 0
    // #define NDEBUG
#endif
// #define __buffer_check__
#define __precision__ 1
#define iostream_untie true
#define debug_stream std::cerr
#include <algorithm>
#include <bitset>
#include <cassert>
#include <chrono>
#include <complex>
#include <cstring>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <unordered_map>
#include <unordered_set>
#include <valarray>
#define all(v) std::begin(v), std::end(v)
#define rall(v) std::rbegin(v), std::rend(v)
#define odd(n) ((n) & 1)
#define even(n) (not __odd(n))
#define __popcount(n) __builtin_popcountll(n)
#define __clz32(n) __builtin_clz(n)
#define __clz64(n) __builtin_clzll(n)
#define __ctz32(n) __builtin_ctz(n)
#define __ctz64(n) __builtin_ctzll(n)
/* preprocessor end */

namespace setting
{
    using namespace std::chrono;
    system_clock::time_point start_time, end_time;
    long long get_elapsed_time() { end_time = system_clock::now(); return duration_cast<milliseconds>(end_time - start_time).count(); }
    void print_elapsed_time() { debug_stream << "\n----- Exec time : " << get_elapsed_time() << " ms -----\n"; }
    void buffer_check() { char bufc; if(std::cin >> bufc) debug_stream << "\n\033[1;35mwarning\033[0m: buffer not empty.\n"; }
    struct setupper
    {
        setupper()
        {
            if(iostream_untie) std::ios::sync_with_stdio(false), std::cin.tie(nullptr);
            std::cout << std::fixed << std::setprecision(__precision__);
    #ifdef stderr_path
            if(freopen(stderr_path, "a", stderr))
            {
                std::cerr << std::fixed << std::setprecision(__precision__);
            }
    #endif
    #ifdef stdout_path
            if(not freopen(stdout_path, "w", stdout))
            {
                freopen("CON", "w", stdout);
                debug_stream << "\n\033[1;35mwarning\033[0m: failed to open stdout file.\n";
            }
            std::cout << "";
    #endif
    #ifdef stdin_path
            if(not freopen(stdin_path, "r", stdin))
            {
                freopen("CON", "r", stdin);
                debug_stream << "\n\033[1;35mwarning\033[0m: failed to open stdin file.\n";
            }
    #endif
    #ifdef LOCAL
            debug_stream << "\n----- stderr at LOCAL -----\n\n";
            atexit(print_elapsed_time);
    #endif
    #ifdef __buffer_check__
            atexit(buffer_check);
    #endif
    #if defined(__clock__) || defined(LOCAL)
            start_time = system_clock::now();
    #endif
        }
    } __setupper; // struct setupper
} // namespace setting
#ifdef __clock__
class
{
    std::chrono::system_clock::time_point built_pt, last_pt; int built_ln, last_ln;
    std::string built_func, last_func; bool is_built = false;
public:
    void build(int crt_ln, const std::string &crt_func)
    {
        is_built = true, last_pt = built_pt = std::chrono::system_clock::now(), last_ln = built_ln = crt_ln, last_func = built_func = crt_func;
    }
    void set(int crt_ln, const std::string &crt_func)
    {
        if(is_built) last_pt = std::chrono::system_clock::now(), last_ln = crt_ln, last_func = crt_func;
        else debug_stream << "[ " << crt_ln << " : " << crt_func << " ] " << "myclock_t::set failed (yet to be built!)\n";
    }
    void get(int crt_ln, const std::string &crt_func)
    {
        if(is_built)
        {
            std::chrono::system_clock::time_point crt_pt(std::chrono::system_clock::now());
            long long diff = std::chrono::duration_cast<std::chrono::milliseconds>(crt_pt - last_pt).count();
            debug_stream << diff << " ms elapsed from" << " [ " << last_ln << " : " << last_func << " ]";
            if(last_ln == built_ln) debug_stream << " (when built)";
            debug_stream << " to" << " [ " << crt_ln << " : " << crt_func << " ]" << "\n";
            last_pt = built_pt, last_ln = built_ln, last_func = built_func;
        }
        else
        {
            debug_stream << "[ " << crt_ln << " : " << crt_func << " ] " << "myclock_t::get failed (yet to be built!)\n";
        }
    }
} myclock; // unnamed class
    #define build_clock() myclock.build(__LINE__, __func__)
    #define set_clock() myclock.set(__LINE__, __func__)
    #define get_clock() myclock.get(__LINE__, __func__)
#else
    #define build_clock() ((void)0)
    #define set_clock() ((void)0)
    #define get_clock() ((void)0)
#endif

namespace std
{
    // hash
    template <class T> size_t hash_combine(size_t seed, T const &key) { return seed ^ (hash<T>()(key) + 0x9e3779b9 + (seed << 6) + (seed >> 2)); }
    template <class T, class U> struct hash<pair<T, U>> { size_t operator()(pair<T, U> const &pr) const { return hash_combine(hash_combine(0, pr.first), pr.second); } };
    template <class tuple_t, size_t index = tuple_size<tuple_t>::value - 1> struct tuple_hash_calc { static size_t apply(size_t seed, tuple_t const &t) { return hash_combine(tuple_hash_calc<tuple_t, index - 1>::apply(seed, t), get<index>(t)); } };
    template <class tuple_t> struct tuple_hash_calc<tuple_t, 0> { static size_t apply(size_t seed, tuple_t const &t) { return hash_combine(seed, get<0>(t)); } };
    template <class... T> struct hash<tuple<T...>> { size_t operator()(tuple<T...> const &t) const { return tuple_hash_calc<tuple<T...>>::apply(0, t); } };
    // iostream
    template <class T, class U> istream &operator>>(istream &is, pair<T, U> &p) { return is >> p.first >> p.second; }
    template <class T, class U> ostream &operator<<(ostream &os, const pair<T, U> &p) { return os << p.first << ' ' << p.second; }
    template <class tuple_t, size_t index> struct tupleis { static istream &apply(istream &is, tuple_t &t) { tupleis<tuple_t, index - 1>::apply(is, t); return is >> get<index>(t); } };
    template <class tuple_t> struct tupleis<tuple_t, SIZE_MAX> { static istream &apply(istream &is, tuple_t &t) { return is; } };
    template <class... T> istream &operator>>(istream &is, tuple<T...> &t) { return tupleis<tuple<T...>, tuple_size<tuple<T...>>::value - 1>::apply(is, t); }
    template <> istream &operator>>(istream &is, tuple<> &t) { return is; }
    template <class tuple_t, size_t index> struct tupleos { static ostream &apply(ostream &os, const tuple_t &t) { tupleos<tuple_t, index - 1>::apply(os, t); return os << ' ' << get<index>(t); } };
    template <class tuple_t> struct tupleos<tuple_t, 0> { static ostream &apply(ostream &os, const tuple_t &t) { return os << get<0>(t); } };
    template <class... T> ostream &operator<<(ostream &os, const tuple<T...> &t) { return tupleos<tuple<T...>, tuple_size<tuple<T...>>::value - 1>::apply(os, t); }
    template <> ostream &operator<<(ostream &os, const tuple<> &t) { return os; }
    template <class Container, typename Value = typename Container::value_type, enable_if_t<!is_same<decay_t<Container>, string>::value, nullptr_t> = nullptr>
    istream& operator>>(istream& is, Container &cont) { for(auto&& e : cont) is >> e; return is; }
    template <class Container, typename Value = typename Container::value_type, enable_if_t<!is_same<decay_t<Container>, string>::value, nullptr_t> = nullptr>
    ostream& operator<<(ostream& os, const Container &cont) { bool flag = 1; for(auto&& e : cont) flag ? flag = 0 : (os << ' ', 0), os << e; return os; }
} // namespace std

/* dump definition start */
#ifdef LOCAL
    #define dump(...) debug_stream << "[ " << __LINE__ << " : " << __FUNCTION__ << " ]\n", dump_func(#__VA_ARGS__, __VA_ARGS__)
    template <class T> void dump_func(const char *ptr, const T &x)
    {
        debug_stream << '\t';
        for(char c = *ptr; c != '\0'; c = *++ptr) if(c != ' ' && c != '\t') debug_stream << c;
        debug_stream << " : " << x << '\n';
    }
    template <class T, class... rest_t> void dump_func(const char *ptr, const T &x, rest_t... rest)
    {
        debug_stream << '\t';
        for(char c = *ptr; c != ','; c = *++ptr) if(c != ' ' && c != '\t') debug_stream << c;
        debug_stream << " : " << x << ",\n"; dump_func(++ptr, rest...);
    }
#else
    #define dump(...) ((void)0)
#endif
/* dump definition end */

/* function utility start */
template <class T, class... types> T read(types... args) noexcept { T obj(args...); std::cin >> obj; return obj; }
#define input(type, var, ...) type var{read<type>(__VA_ARGS__)}
// substitute y for x if x > y.
template <class T> inline bool sbmin(T &x, const T &y) { return x > y ? x = y, true : false; }
// substitute y for x if x < y.
template <class T> inline bool sbmax(T &x, const T &y) { return x < y ? x = y, true : false; }
// binary search on discrete range.
template <class iter_type, class pred_type>
iter_type binary(iter_type __ok, iter_type __ng, pred_type pred)
{
    std::ptrdiff_t dist(__ng - __ok);
    while(abs(dist) > 1)
    {
        iter_type mid(__ok + dist / 2);
        if(pred(mid)) __ok = mid, dist -= dist / 2;
        else __ng = mid, dist /= 2;
    }
    return __ok;
}
// binary search on real numbers.
template <class pred_type>
long double binary(long double __ok, long double __ng, const long double eps, pred_type pred)
{
    while(abs(__ok - __ng) > eps)
    {
        long double mid{(__ok + __ng) / 2};
        (pred(mid) ? __ok : __ng) = mid;
    }
    return __ok;
}
// reset all bits.
template <class A> void reset(A &array) { memset(array, 0, sizeof(array)); }
// be careful that val is type-sensitive.
template <class T, class A, size_t N> void init(A (&array)[N], const T &val) { std::fill((T*)array, (T*)(array + N), val); }
/* functon utility end */

/* using alias start */
using namespace std;
using i32 = int_least32_t; using i64 = int_least64_t; using u32 = uint_least32_t; using u64 = uint_least64_t;
using pii = pair<i32, i32>; using pll = pair<i64, i64>;
template <class T> using heap = priority_queue<T>;
template <class T> using rheap = priority_queue<T, vector<T>, greater<T>>;
template <class T> using hashset = unordered_set<T>;
template <class Key, class Value> using hashmap = unordered_map<Key, Value>;
/* using alias end */

/* library start */

#ifndef Strongly_connected_components_hpp
#define Strongly_connected_components_hpp
#include <vector>

class Strongly_connected_components
{
    const size_t V;
    std::vector<std::vector<size_t>> adj, mem;
    std::vector<size_t> comp, low;
    size_t n;
    bool is_built;

public:
    Strongly_connected_components(size_t _V) : V(_V), adj(V), comp(V), low(V), is_built() {}

    // add an edge from the vertex s to the vertex t.
    void add_edge(size_t s, size_t t) { adj[s].emplace_back(t); is_built = false; }

    // the number of the components.
    size_t count() { return build(), n; }

    // the number of vertices in the i-th component.
    size_t size(size_t i) { return build(), mem[i].size(); }

    // vertices in the i-th component.
    const std::vector<size_t> &component(size_t i) { return build(), mem[i]; }

    // the component which the vertex v belongs to.
    size_t operator[](size_t v) { return build(), comp[v]; }

    // the directed acyclic graph consisting of the components.
    std::vector<std::vector<size_t>> make_dag()
    {
        build();
        std::vector<std::vector<size_t>> res(n);
        bool *apr = new bool[V]{};
        size_t *stack_ptr = new size_t[V];
        for(size_t i = 0; i != n; ++i)
        {
            size_t *itr = stack_ptr;
            for(size_t s : mem[i]) for(size_t t : adj[s]) if(!apr[comp[t]]) apr[comp[t]] = true, *itr++ = comp[t];
            res[i].resize(itr - stack_ptr);
            while(itr != stack_ptr) apr[res[i][--itr - stack_ptr] = *itr] = false;
        }
        delete[] apr; delete[] stack_ptr;
        return res;
    }

protected:
    void build()
    {
        if(is_built) return;
        is_built = true, n = 0;
        fill(low.begin(), low.end(), -1);
        fill(comp.begin(), comp.end(), -1);
        size_t *itr = new size_t[V];
        for(size_t v = 0, c = 0; v != V; ++v) affix(v, c, itr);
        delete[] itr; mem.resize(n);
        for(size_t v = 0; v != V; ++v) mem[comp[v] = n - 1 - comp[v]].emplace_back(v);
    }

    size_t affix(size_t v, size_t &c, size_t* &itr)
    {
        if(~low[v]) return ~comp[v] ? -1 : low[v];
        size_t idx = c++; low[v] = idx; *itr++ = v;
        for(int u : adj[v]) low[v] = std::min(low[v], affix(u, c, itr));
        if(low[v] == idx) { do { comp[*--itr] = n; } while(*itr != v); ++n; }
        return low[v];
    }
}; // class Strongly_connected_components

#endif // Strongly_connected_components_hpp


/* library end */

/* The main code follows. */

struct solver
{
    solver()
    {
        input(int,n);
        Strongly_connected_components scc(n);
        vector<int> l(n);
        int sum=0;
        for(int i=0; i<n; ++i)
        {
            cin>>l[i];
            sum+=l[i];
            input(int,s); --s;
            scc.add_edge(s,i);
        }
        auto dag(scc.make_dag());
        bool in[111]={};
        for(int i=0; i<dag.size(); ++i)
        {
            if(!in[i])
            {
                int min_l=1e5;
                for(int v : scc.component(i))
                {
                    sbmin(min_l,l[v]);
                }
                sum+=min_l;
            }
            for(int to : dag[i])
            {
                in[to]=1;
            }
        }
        cout << (double)sum/2 << "\n";
    }
}; // struct solver

int main(int argc, char *argv[])
{
    u32 t; // loop count
#ifdef LOCAL
    t = 1;
#else
    t = 1; // single test case
#endif
    // t = -1; // infinite loop
    // cin >> t; // case number given

    while(t--)
    {
        solver();
    }
}