#include <iostream>
#include <fstream>
using namespace std;

int main(){
    ifstream in("flip.in");
    ofstream out("flip.out");
    int c,r;
    long long int sum = 0;
    in >> r >>c;
    int m[r][c];
    bool ok = false;
    for(int i =1; i<=r;i++)
        for(int h=1;h<=c;h++){
            in >> m[i][h];
            if(m[i][h] >= 0){
                sum += m[i][h];
                if(m[i][h] == 0)
                    ok = true;
            }
        }

    if(ok || sum > 0){
        out << sum;
        return 0;
    }
    else{
        sum = m[1][1];
        for(int i =1;i<=r;i++)
            for(int j =1;j<=c;j++)
                if(sum > m[i][j])
                    {
                        sum = m[i][j];
                    }
    }
    out << sum;
/*
            for(int ii =i;ii<=r;ii++)
                for(int jj=j;jj<=c;jj++)
                    if(m[i][j] > m[ii][jj]){
                        int aux = m[ii][jj];
                        m[ii][jj] = m[i][j];
                        m[i][j] = aux;
                    }
*/



    return 0;

}