#include <stdio.h>


int main(){

    freopen("flip.in", "r", stdin);
    freopen("flip.out", "w", stdout);

    int x, y, c;
    scanf("%d%d", &x, &y);

    int v[x][y], i, j;
    for(i = 0; i < x; i++)
        for(j = 0; j < y; j++)
            scanf("%d", &v[i][j]);

    int sum = 0;

    for(i = 0; i < x; i++){
        for(j = 0; j < y; j++)
            sum += v[i][j];
        if(sum < 0){
            for(j = 0; j < y; j++)
                v[i][j] *= -1;
        }
        sum = 0;
    }
    for(j = 0; j < y; j++){
        for(i = 0; i < x; i++)
            sum += v[i][j];
        if(sum < 0){
            for(i = 0; i < x; i++)
                v[i][j] *= -1;
        }
        sum = 0;

    }

/*  printf(" %d %d\n",x,y);
 *  for (i = 0; i < x; i++){
 *      for (j = 0; j < y; j++)
 *          printf("v[%d][%d] = %d ",i,j,v[i][j]);
 *      printf("\n");
 *  }
 */


    sum = 0;
    for (i = 0; i < x; i++)
        for (j = 0; j < y; j++)
            sum += v[i][j];

    printf("%d",sum);
    return 0;
}