#include<iostream.h>
#include<stdio.h>
FILE *f=fopen("flip.in","r"),*g=fopen("flip.out","w");
 int main()
{
long a[100][100],m,n,i,j,k,d=0,s=0,s1=0,v[1000];
int t=1,t1=1,t3=1;
 fscanf(f,"%ld %ld\n",&m,&n);
for(i=1;i<=n;i++)
for(j=1;j<=m;j++)
fscanf(f,"%ld ",&a[i][j]);
 for(i=1;i<=n;i++)
{
s=0;
s1=0;
t=1;
t1=1;
d=0;
t3=1;
for(j=1;j<=m;j++)
s+=a[i][j];
if(s<0) t=0;
if(!t)
{
for(k=1;k<=m;k++)
{
s1=0;
for(j=1;j<=n;j++)
s1+=a[j][k];
if(s1<0)
{
t1=0;
for(j=1;j<=n;j++)
{
a[j][k]=a[j][k]*-1;
if(j==i)
{
d++;
v[d]=k;
}
}
}
}
}
if(!t1)
{
for(j=1;j<=m;j++)
{
t3=1;
for(k=1;k<=d&&t3;k++)
if(j==v[k]) t3=0;
if(t3) a[i][j]=a[i][j]*-1;
}
}
}
s=0;
for(i=1;i<=n;i++)
 for(j=1;j<=m;j++)
s+=a[i][j];
 fprintf(g,"%ld",s);
return 0;
}