#include<stdio.h>
int main()
{
	freopen("flip.in","r",stdin);
	freopen("flip.out","w",stdout);
	int n, m, a[17][17], i, j;
	scanf("%d%d",&n,&m);
	for(i=1;i<=n;i++)
		for(j=1;j<=m;j++)
			scanf("%d", &a[i][j]);
	int s=0;
	//Pentru ca suma sa fie maxima, toate elmentele trebuiesc sa fie >=0;
	for(i=1;i<=n;i++)
		for(j=1;j<=m;j++)
			if(a[i][j]<0)
			s+=(-a[i][j]);
			else
			s+=a[i][j];
	printf("%d",s);
	return 0;
}