local n = io.read("*n")
local a = {}
for i = 1, n * 2 do
  a[i] = io.read("*n")
end
table.sort(a)
local ret = 0
for i = 1, n * 2, 2 do
  ret = ret + a[i] * a[i + 1]
end
ret = tostring(1LL * ret):gsub("LL", "")
print(ret)