using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;

class C {
    static StreamWriter Out = new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
    static void Main(string[] args) {
        long N;
        Input(out N);
        long[] A;
        Inputs(out A);
        Dictionary<long, long> count = new Dictionary<long, long>();
        for(long i = 0; i < N; i++) {
            if(count.ContainsKey(A[i])) {
                count[A[i]]++;
            } else {
                count.Add(A[i], 1);
            }
        }
        long x = 0;
        long y = 0;
        foreach(var item in count) {
            long len = item.Key;
            long c = item.Value;
            if(2 <= c) {
                if(c < 4) {
                    if(x < len) {
                        if(y < x) {
                            y = x;
                        }
                        x = len;
                    } else if(y < len) {
                        if(x < y) {
                            x = y;
                        }
                        y = len;
                    }
                } else {
                    if(x * y < len * len) {
                        x = len;
                        y = len;
                    }
                }
            }
        }
        Print(x * y);
        Out.Flush();
    }
    static T ChangeT<T>(string s) => (T)Convert.ChangeType(s, typeof(T));
    static void Input<A>(out A a) {
        var words = Console.ReadLine().Split(new[] { ' ' }, options: StringSplitOptions.RemoveEmptyEntries);
        a = ChangeT<A>(words[0]);
    }
    static void Input<A, B>(out A a, out B b) {
        var words = Console.ReadLine().Split(new[] { ' ' }, options: StringSplitOptions.RemoveEmptyEntries);
        a = ChangeT<A>(words[0]);
        b = ChangeT<B>(words[1]);
    }
    static void Input<A, B, C>(out A a, out B b, out C c) {
        var words = Console.ReadLine().Split(new[] { ' ' }, options: StringSplitOptions.RemoveEmptyEntries);
        a = ChangeT<A>(words[0]);
        b = ChangeT<B>(words[1]);
        c = ChangeT<C>(words[2]);
    }
    static void Input<A, B, C, D>(out A a, out B b, out C c, out D d) {
        var words = Console.ReadLine().Split(new[] { ' ' }, options: StringSplitOptions.RemoveEmptyEntries);
        a = ChangeT<A>(words[0]);
        b = ChangeT<B>(words[1]);
        c = ChangeT<C>(words[2]);
        d = ChangeT<D>(words[3]);
    }
    static void Input<A, B, C, D, E>(out A a, out B b, out C c, out D d, out E e) {
        var words = Console.ReadLine().Split(new[] { ' ' }, options: StringSplitOptions.RemoveEmptyEntries);
        a = ChangeT<A>(words[0]);
        b = ChangeT<B>(words[1]);
        c = ChangeT<C>(words[2]);
        d = ChangeT<D>(words[3]);
        e = ChangeT<E>(words[4]);
    }
    static void Input<A, B, C, D, E, F>(out A a, out B b, out C c, out D d, out E e, out F f) {
        var words = Console.ReadLine().Split(new[] { ' ' }, options: StringSplitOptions.RemoveEmptyEntries);
        a = ChangeT<A>(words[0]);
        b = ChangeT<B>(words[1]);
        c = ChangeT<C>(words[2]);
        d = ChangeT<D>(words[3]);
        e = ChangeT<E>(words[4]);
        f = ChangeT<F>(words[5]);
    }
    static void Inputs<T>(out T[] array) {
        array = Console.ReadLine().Split(new[] { ' ' }, options: StringSplitOptions.RemoveEmptyEntries).Select(s => ChangeT<T>(s)).ToArray();
    }
    static void Print<T>(T s) => Out.WriteLine(s);
    static void Print<T>(params T[] s) => Out.WriteLine(string.Join(" ", s));
    static void Print<T>(IEnumerable<T> e) => Out.WriteLine(string.Join(" ", e));
}

Measured memory_bytes: 32092