#include<stdio.h>
#include<math.h>


int main()
{
	freopen("flip.in","r",stdin);
	freopen("flip.out","w",stdout);

	int n,m,a[100][100];
	int i,j;

	scanf("%d%d",&n,&m);
	

	for(i = 0;i < n;i++){
		for(j = 0;j < m;j++){	
			scanf("%d",&a[i][j]);
		}
	}

	int s=0;

	for(i = 0;i < n;i++){
                for(j = 0;j < m;j++){
			if(a[i][j] > 0){
			
			s = s + a[i][j];
			
			}
		}
	}

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

	for(i = 0;i < n;i++){
                for(j = 0;j < m;j++){
			if(a[i][j] > 0){

			s1 = s1 + a[i][j];
			
			}
		}
	}		

	if(s1 < s){
		printf("%d\n",s);
	}else{
		printf("%d\n",s1);
	}
/*	printf("\n %d \n",s1);	

//	printf("\n%d\n",s);
//	printf("")
	
	int k = 0;
	 for(i = 0;i < n;i++){   
                for(j = 0;j < m;j++){     
                        printf("%d ",a[i][j]);
				k++;
			if(k == m){
				printf("\n");
				k = 0;
			}
		}
	}
*/
	return 0;
}