cherry

#include<bits/stdc++.h>
using namespace std;
#define rep(i,j,k) for(int i=j;i<k;i++)
int n,grid[102][102],dp[102][102];

int fun(int r1,int c1,int c2)
{
    int r2 = r1 + c1 - c2;
    if (n == r1 || n == r2 || n == c1 || n == c2 ||
                grid[r1][c1] == -1 || grid[r2][c2] == -1)
            return -9999999;
    if (r1 == n-1 && c1 == n-1)
            return grid[r1][c1];
    if(dp[r1][c1][c2]!=INT_MIN) return dp[r1][c1][c2];
    int ans=grid[r1][c1];
    if (c1 != c2) ans += grid[r2][c2];
            ans += Math.max(Math.max(dp(r1, c1+1, c2+1), dp(r1+1, c1, c2+1)),
                            Math.max(dp(r1, c1+1, c2), dp(r1+1, c1, c2)));
            memo[r1][c1][c2] = ans;
            return ans;
}
int main()
{
    cin>>n;
    rep(i,0,n) rep(j,0,n) cin>>grid[i][j];
    rep(i,0,n) rep(j,0,n) rep(k,0,n) dp[i][j][k]=INT_MIN;
    int ans=fun(0,0,0);
    cout<<max(ans,0);
    return 0;
}