import * as fs from "fs"

const main = (args: string): void => {
    const input = args.trim().split("\n");
    const N = parseInt(input.shift())
    const A = input.shift().split(" ").map(x => Number(x))
    A.sort((x, y) => x > y ? -1 : 1)
    let ans = BigInt(0)

    for (let i = 0; i < 2 * N; i += 2) {
        ans += BigInt(A[i] * A[i + 1])
    }
    console.log(String(ans))
}

main(fs.readFileSync('/dev/stdin', 'utf8'));

function apply<T, R>(value: T, func: (arg: T) => R): R {
    return func(value)
}