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# include <bits/stdc++.h>
using namespace std ;
typedef long long LL ;
const int N = 1010 ;
const LL INF = 1e18 ;
LL f [ N ] [ N ] [ 3 ] ;
LL a [ N ] [ N ] ;
int n , m ;
int main ( ) {
cin > > n > > m ;
for ( int i = 1 ; i < = n ; i + + )
for ( int j = 1 ; j < = m ; j + + ) {
cin > > a [ i ] [ j ] ;
f [ i ] [ j ] [ 0 ] = f [ i ] [ j ] [ 1 ] = f [ i ] [ j ] [ 2 ] = - INF ;
}
// 初始化
f [ 1 ] [ 1 ] [ 0 ] = f [ 1 ] [ 1 ] [ 1 ] = a [ 1 ] [ 1 ] ;
for ( int i = 2 ; i < = n ; i + + ) f [ i ] [ 1 ] [ 1 ] = f [ i - 1 ] [ 1 ] [ 1 ] + a [ i ] [ 1 ] ;
for ( int j = 2 ; j < = m ; j + + ) {
for ( int i = 1 ; i < = n ; i + + )
f [ i ] [ j ] [ 0 ] = max ( { f [ i ] [ j - 1 ] [ 1 ] , f [ i ] [ j - 1 ] [ 0 ] , f [ i ] [ j - 1 ] [ 2 ] } ) + a [ i ] [ j ] ;
for ( int i = 2 ; i < = n ; i + + )
f [ i ] [ j ] [ 1 ] = max ( f [ i - 1 ] [ j ] [ 0 ] , f [ i - 1 ] [ j ] [ 1 ] ) + a [ i ] [ j ] ;
for ( int i = n - 1 ; i > = 1 ; i - - )
f [ i ] [ j ] [ 2 ] = max ( f [ i + 1 ] [ j ] [ 0 ] , f [ i + 1 ] [ j ] [ 2 ] ) + a [ i ] [ j ] ;
}
cout < < max ( f [ n ] [ m ] [ 0 ] , f [ n ] [ m ] [ 1 ] ) ;
// 1e3 * 1e3 * 1e4=1e10=10000000000>2147483647 因为 1e10是11位数， ，
return 0 ;
}
