#include <stdio.h>
#include <stdlib.h>
int main()
{
     unsigned h,w, max;
     scanf("%u%u",&h,&w);
     unsigned (*buf)[w+2] = malloc(sizeof(unsigned)*h*(w+2));
     for (unsigned j = 0; j < h; j++) {
	  buf[j][0] = buf[j][w+1] = 0;
	  for (unsigned i = 1; i <= w; i++){
	       scanf("%d",&buf[j][i]);
	  }
     }
/*/
     for (unsigned j = 0; j < h; j++) {
	  for (unsigned i = 0; i <= w+1;i++){
	       printf("%d ",buf[j][i]);
	  }
	  printf("\n");
     }
*/
     for (unsigned j = 1; j < h; j++) {
	  for (unsigned x = 1; x <= w; x++) {
	       unsigned *maxp = &buf[j-1][x];
	       max = maxp[0] < maxp[-1] ? maxp[-1] : maxp[0];
	       if (max < maxp[1]) max = maxp[1];
	       buf[j][x] += max;
	  }
/*/
	  for (unsigned i = 1; i <= w; i++){
	       printf("%d ",buf[j][i]);
	  }
	  printf("\n");
 
*/
     }
     max = buf[h-1][0];
     for (unsigned i = 1; i <= w; i++)
	  if (max < buf[h-1][i]) max = buf[h-1][i];
     printf("%u\n",max);
     return 0;
}
 

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