#include <fstream>
#include <cmath>
using namespace std;
ifstream cin("flip.in");
ofstream cout("flip.out");
int v[300];
int main(){
     int n,m,sum = 0;
     cin >> n >> m;
     for(int i = 0; i <= n*m; i++){
 		cin >> v[i];
 		int x = v[i];
 		if(x >= 0){
 			sum = sum + x;
 		}else{
 			sum = sum + abs(x);
 		}	
     }
     cout << sum;


	return 0;
}