"use strict"
const create = () => {
    const input = require("fs").readFileSync("/dev/stdin", "utf8").trim().split("\n");
    const res = {
        "list": input, "index": 0, "max": input.length,
        "hasNext": function () { return this.index < this.max },
        "next": function () { if (!this.hasNext()) { throw "ArrayIndexOutOfBoundsException"; } else { return this.list[this.index++]; } }
    };
    return res;
}
const o = create();
const next = () => o.next()
const nextInt = () => parseInt(o.next())
const nextStrArray = () => o.next().split(" ")
const nextIntArray = () => o.next().split(" ").map(el => parseInt(el))
const nextCharArray = () => o.next().split("")
const hasNext = () => o.hasNext()
const myout = (...x) => console.log(...x)
const Main = () => {
    let n = nextInt()
    let a = nextIntArray()
    a.sort((a, b) => b - a)
    let m = {}
    let one = 0
    let two = 0
    for (let i = 0; i < a.length; i++) {
        if (!m[a[i]]) m[a[i]] = 1
        else {
            if (one == 0) {
                one = a[i]
                m[a[i]] = 0
            } else {
                two = a[i]
                break
            }
        }
    }
    console.log((BigInt(one) * BigInt(two)).toString())
}
Main()

