#!/usr/bin/env python3
import sys

def main():
    N = int(input())
    A = list(map(int, input().split()))
    A.sort()
    ans = 0
    for k in range(N):
        ans += A[2 * k] * A[2 * k + 1]
    print(ans)

if __name__ == '__main__':
    main()