/*
 * flip.c
 *
 *  Created on: 09.04.2013
 *      Author: Alex
 */

#include <stdio.h>
#include <stdlib.h>

int main()
{
	FILE *f1=fopen("flip.in", "r");
	FILE *f2=fopen("flip.out", "w");
	int i,j;
	long N,M,a[100][100], suma=0;
	fscanf(f1, "%ld%ld", &N, &M);
	for(i=0; i<N; ++i)
	{
		for(j=0; j<M; ++j)
		{
			fscanf(f1, "%ld", &a[i][j]);
			if(a[i][j] < 0)
			{
				a[i][j]=-a[i][j];
			}
			suma=suma+a[i][j];
		}
	}
	fprintf(f2, "%ld", suma);
	fclose(f1);
	fclose(f2);
	return 0;
}