//det suma matrice
#include<fstream.h>

int a[101][101];

ifstream in("flip.in");
ofstream out("flip.out");

int main()
{
	int n,m,i,s=0,j,s1=0;

	in>>n>>m;
	for(i=1;i<=n;i++)
		for(j=1;j<=m;j++)
			in>>a[i][j];

	for(i=1;i<=n;i++)
	{
		s=0;
		for(j=1;j<=m;j++)
		{
			if(a[i][j]<0)
            a[i][j]*=-1;
			s+=a[i][j];
		}
		s1+=s;
	}
    out<<s1;
	return 0;
}