```go
package main

import (
	"bufio"
	"fmt"
	"math"
	"os"
	"strconv"
)

func max(a, b int) int {
	if a > b {
		return a
	}
	return b
}

func main() {
	scanner := bufio.NewScanner(os.Stdin)
	scanner.Split(bufio.ScanWords)
	
	scanner.Scan()
	n, _ := strconv.Atoi(scanner.Text())
	
	grid := make([][]int, n)
	for i := 0; i < n; i++ {
		grid[i] = make([]int, n)
		for j := 0; j < n; j++ {
			scanner.Scan()
			grid[i][j], _ = strconv.Atoi(scanner.Text())
		}
	}
	
	dp := make([][]int, n)
	newDp := make([][]int, n)
	for i := 0; i < n; i++ {
		dp[i] = make([]int, n)
		newDp[i] = make([]int, n)
		for j := 0; j < n; j++ {
			dp[i][j] = math.MinInt64
		}
	}
	dp[0][0] = grid[0][0]
	
	for t := 1; t <= 2*n-2; t++ {
		for i := 0; i < n; i++ {
			for j := 0; j < n; j++ {
				newDp[i][j] = math.MinInt64
			}
		}
		
		minI := t - (n - 1)
		if minI < 0 {
			minI = 0
		}
		maxI := t
		if maxI > n-1 {
			maxI = n - 1
		}
		
		for i1 := minI; i1 <= maxI; i1++ {
			j1 := t - i1
			for i2 := minI; i2 <= maxI; i2++ {
				j2 := t - i2
				
				val := grid[i1][j1]
				if i1 != i2 {
					val += grid[i2][j2]
				}
				
				best := math.MinInt64
				
				if i1 > 0 && i2 > 0 {
					best = max(best, dp[i1-1][i2-1])
				}
				if i1 > 0 && i2 <= t-1 {
					best = max(best, dp[i1-1][i2])
				}
				if i1 <= t-1 && i2 > 0 {
					best = max(best, dp[i1][i2-1])
				}
				if i1 <= t-1 && i2 <= t-1 {
					best = max(best, dp[i1][i2])
				}
				
				if best != math.MinInt64 {
					newDp[i1][i2] = best + val
				}
			}
		}
		dp, newDp = newDp, dp
	}
	
	fmt.Println(dp[n-1][n-1])
}
```