func hourglassSum(_ arr: [[Int]]) -> Int {
var ans = Int.min
for i in 0..<arr.count-2 {
for j in 0..<arr[i].count-2 {
var sum = arr[i][j] + arr[i][j+1] + arr[i][j+2]
sum += arr[i+1][j+1]
sum += arr[i+2][j] + arr[i+2][j+1] + arr[i+2][j+2]
ans = max(ans, sum)
}
}
return ans
}