#include <stdio.h>
#include <fstream>
using namespace std;
long int i,j,s,m,n,z;
int main()
{
    FILE*f;
    f=fopen("flip.in","r");
    fscanf(f,"%li%li",&n,&m);
    for(i=0;i<n;i++)
        for(j=0;j<m;j++)
        {
        fscanf(f,"%li",&z);
        if(z<0) z=-1*z;
        s+=z;
        }
    FILE*g;
    g=fopen("flip.out","w");
    fprintf(g,"%li",s);
    fclose(f);
    fclose(g);

    return 0;
}