#include<iostream.h>
#include<stdio.h>
int main ()
{int M,N,cm,cn;
long int m[16][16];
long long S;
freopen("flip.in", "rt", stdin);
freopen("flip.out", "wt", stdout);
scanf ("%d",&N);
scanf ("%d",&M);
for (cn=0;cn<N;cn++) for (cm=0;cm<M;cm++) scanf ("%ld",&m[cn][cm]);
for (cm=0;cm<M;cm++) {S=0;
                      for (cn=0;cn<N;cn++) S=S+m[cn][cm];
		      if (S<0) for (cn=0;cn<N;cn++) m[cn][cm]=m[cn][cm]*(-1);}
for (cn=0;cn<N;cn++) {S=0;
                      for (cm=0;cm<M;cm++) S=S+m[cn][cm];
                      if (S<0) for (cm=0;cm<M;cm++) m[cn][cm]=m[cn][cm]*(-1);}
S=0;
for (cn=0;cn<N;cn++) for (cm=0;cm<M;cm++) S=S+m[cn][cm];
printf ("%lld", S);
return 0;}