#include<stdio.h>

int main()
{
 int a[50][50],m,n,i,j,sp,sn,ok=0;
 freopen("flip.in","r",stdin);
 freopen("flip.out","w",stdout);
 scanf("%d",&n);
 scanf("%d",&m);
 for(i=1;i<=n;i++)
  for(j=1;j<=m;j++)
   scanf("%d",&a[i][j]);
 do
  {
   ok=1;
   for(i=1;i<=n;i++)
    {
     sp=0;sn=0;
     for(j=1;j<=m;j++)
    if(a[i][j]>=0)
     sp=sp+a[i][j];
      else
       sn=sn+a[i][j];
     if(sn*-1>sp)
      {for(j=1;j<=m;j++)
    a[i][j]=a[i][j]*-1;
       ok=0;
      }
    }
   for(j=1;j<=m;j++)
   {
     sp=0;sn=0;
     for(i=1;i<=n;i++)    
    if(a[i][j]>=0)
     sp=sp+a[i][j];
      else
       sn=sn+a[i][j];
     if(sn*-1>sp)
      {for(i=1;i<=n;i++)
    a[i][j]=a[i][j]*-1;
       ok=0;
      }
    }
     
  }
  while(ok==0);
 sp=0;
 for(i=1;i<=n;i++)
  for(j=1;j<=m;j++)
   sp=sp+a[i][j];
 printf("%d",&sp);
 return 0;
}