#include <stdio.h>
#include <stdlib.h>
#include <vector>
#include <unistd.h>
#include <string.h>

int recursiveN2(int posX, int max, std::vector<std::vector<int>> matrix, int sum) {
    sum += matrix[matrix.size()-1][posX];
    if(posX < max - 1) {
        sum = recursiveN2(posX+1,max,matrix, sum);
    }
    return sum;
}

int recursiveN1(int posX, int max, std::vector<std::vector<int>> matrix, int sum) {
    int sum1 = 0;
    int sum2 = 0;
    sum += matrix[matrix.size()-2][posX];
    printf("%d\n",sum);
    if(posX > 0) {
        sum1 = recursiveN1(posX-1, max, matrix, sum);
    }
    sum2 = recursiveN2(posX,max,matrix, sum);

    return (sum1 > sum2) ? sum1 : sum2;
}

int recursiveN3(int posX, int posY, int max, std::vector<std::vector<int>> matrix, int sum) {
    sum += matrix[posY][posX];
    if(posX == max-1 && posY == 1) {
        return sum;
    }
    int sum1 = -10000000;
    int sum2 = -10000000;
    if(posY == 0) {
        sum1 = recursiveN3(posX,posY+1,max,matrix,sum);
    }
    if(posX < max -2) {
        sum2 = recursiveN3(posX+1,posY,max,matrix,sum);
    } 

    return (sum1 > sum2) ? sum1 : sum2;

}

int main() {
    int numOfRow, numOfCol;
    char buffer[1024];
    std::vector<std::vector<int>> matrix;
    std::vector<int> row;
    char* token;

    read(1,buffer,sizeof(buffer));
    sscanf(buffer,"%d %d",&numOfRow, &numOfCol);

    for(int i = 0; i < numOfRow; i++) {
        read(1,buffer,sizeof(buffer));
        for(int k = 0; k < numOfCol; k++) {
            if( k == 0 ) {
                token = strtok(buffer," ");
            } else if(k!= numOfCol - 1) {
                token = strtok(NULL," ");
            } else {
                token = strtok(NULL,"\n");
            }
            
            row.push_back(atoi(token));

        }
        
        matrix.push_back(row);
        row.erase(row.begin(),row.end());
    }

    int posX = 0, posY = 0;
    int max = 0;
    int dir = 0;
    int sum = 0;


    for(int i = 0; i < numOfRow - 2; i++) {
        for(int k = 0; k < numOfCol; k++) {
            sum += matrix[i][k];
        }
    }

    if(numOfRow ==  2) {
        if(numOfCol % 2 == 1) sum = recursiveN1(numOfCol-1,numOfCol,matrix,sum);
        else {
            sum = recursiveN3(numOfCol-2, 0,numOfCol,matrix,sum);
        }
    }else {
        sum = recursiveN1(numOfCol-1,numOfCol,matrix,sum);
    }

    posX = numOfCol - 1;
    posY = numOfRow - 2;

    printf("%d\n",sum);

    return 0;
}