# Uses python3

bigger = 0
biggest = 0

n = int(input())
a = [int(x) for x in input().split()]

for i in range(n):
    if a[i] > biggest:
        bigger = biggest
        biggest = a[i]
    elif a[i] == biggest:
        bigger = a[i]
    elif a[i] > bigger:
        bigger = a[i]  

print(bigger * biggest)