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

int main()
{
	FILE *input, *output;
	input = fopen("flip.in", "r");
	output = fopen("flip.out", "w");
	int M, N;
	
	fscanf(input, "%d", &N);
	fscanf(input, "%d", &M);

	int i, j;
	int v[N][M];
	
	for(i = 0; i < N; i++)
	{
		for(j = 0; j < M; j++)
		{
			fscanf(input, "%d", &v[i][j]);
		}
	}
	
	int s;
	
	j = M;
	while(j)
	{
		s = 0;
		for(i = 0; i < N; i++)
		{
			s += v[i][j];
		}
		
		if (s < 0)
		for(i = 0; i < N; i++)
		{
			v[i][j] = -v[i][j];
		}
		j--;
	}
	
	i = N;
	while(i)
	{
		s = 0;
		for(j = 0; j < M; j++)
		{
			s += v[i][j];
		}
		
		if (s < 0)
		for(j = 0; j < M; j++)
		{
			v[i][j] = -v[i][j];
		}
		i--;
	}
	
	int suma = 0;
	for(i = 0; i < N; i++)
	{
		for(j = 0; j < M; j++)
		{
			suma = suma + v[i][j];
		}
	}
	fprintf(output,"%d", suma);
	
	fclose(input);
	fclose(output);
	return 0;
}