#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX(a,b) ((a) > (b) ? (a) : (b))

int main(void){
    int n, m;
    scanf("%d %d", &n, &m);
    long long  int mas[n+2][m+2], d[n+2][m+2];
    int i = 0, j = 0;
    for (; i < n + 2; i++){
        for(j = 0; j < m + 2; j++){
            d[i][j] =0;
        }
    }
    for( i= 0; i < n; i++)
        for (j= 0; j < m; j++)
            scanf("%lld", &mas[i][j]);

    for ( i = 1; i < n+1; i++){
        d[i][1] = mas[i - 1][0];

    }
    for (j = 2; j < m+1; j++){
        for (i = 1; i < n + 1; i++)
            d[i][j] = mas[i - 1][j-1] + MAX(MAX(d[i-1][j-1], d[i+1][j-1]), d[i][j-1]);
    }
    //
    long long int lm = 0;
    for( i= 1; i < n+1; i++){
        if (d[i][m]  > lm) lm = d[i][m];

    }
    printf("%lld", lm);


}