min1,min22,min4,min12 = 1001,1001,1001,1001
n = int(input())
R = 1001**2
for i in range (n):
    x = int(input())
    if (x<min12) and (x%4!=0) and (x%2 ==0):
        min22=min12
        min12=x
    elif (x<min22) and (x%4!=0) and (x%2 ==0):
        min22=x
    elif (x<min4) and (x%4==0):
        min1=min4
        min4=x
    elif(x<min1):
        min1=x
if (min12!=1001 and min22!=1001) and (min22*min12<R):
    R = min12*min22
if (min1!=1001 and min4!=1001) and (min1*min4<R):
    R = min1*min4
else:
    R = -1

print (R)