#include <stdio.h>
#include <stdlib.h>
FILE *in,*out;
int N,M,S,S1,i,j;
int a[17][17];
int main()
{
in=fopen("flip.in","rt");
out=fopen("flip.out","wt");

fscanf(in,"%d%d",&N,&M);

for(i=1;i<=N;i++)
    for(j=1;j<=M;j++)
        fscanf(in,"%d",&a[i][j]);

for(i=1;i<=N;i++)
    for(j=1;j<=M;j++)
    {
        if(a[i][j]>0)
            S=S+a[i][j];
    }
for(i=1;i<=N;i++)
    for(j=1;j<=M;j++)
    {
        a[i][j]=a[i][j]*(-1);
        if(a[i][j]>0)
            S1=S1+a[i][j];
    }
if(S>S1)
    fprintf(out,"%d",S);
else
    fprintf(out,"%d",S1);

    return 0;
}