#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;}