758 B | 758 chars
import sys
from math import sqrt, pi, sin, factorial, ceil, floor
from datetime import datetime, timedelta
BLANK = " "
inp = input
# inp = lambda : sys.stdin.readline()[:-1].strip()
mii = lambda x = BLANK : [*map(int,inp().split(x))]
mfi = lambda x = BLANK : [*map(float,inp().split(x))]
ii = lambda : int(inp())
fi = lambda : float(inp())
p = print
def f(n, l, crt):
if n == 2:
return crt
if n == 3:
return crt + l[0] * l[2]
mx = 0
for i in range(1, n - 1):
l2 = l[:i] + l[i+1:]
k = f(n - 1, l2, crt + l[i - 1] * l[i + 1])
mx = max(mx, k)
return mx
def solve():
n = ii()
l = mii()
k = f(n, l, 0)
p(k)
if __name__ == "__main__":
tc = 1
for t in range(1, tc+1):
ret = solve()