#include <fstream>
using namespace std;
int main()
{int k,n,m,i,j,s,min,a;
ifstream f("flip.in");
ofstream g("flip.out");
int v[100][100];
f>>n;
f>>m;
i=0;
s=0;
while(i<=n)
{i++;
    j=1;
    min=100000000000000000000;
    while(j<=m)
    {f>>v[i][j];
    k=v[i][j];
    if(k<0)
    k=k*(-1);
    if(min>k)
    min=k;
    s=s+k;
j++;}
s=s-(2*min);}
g<<s;
return 0;
}