#include<stdio.h>

int main()
{
 long a[100][100],m,n,i,j,ok,s=0;
 freopen("flip.in","rt",stdin);
 freopen("adunare.out","wt",stdout);

 scanf("%ld%ld",&n,&m);
 
 for(i=0;i<n;i++)
 for(j=0;j<n;j++)
 {cin<<a[i][j];
 ok=1;}
 for(i=0;i<n;i++)
 for(j=0;j<m;j++)
 if(a[i][j]>=0)
 s=s+a[i][j];
 else
 {ok=0;
 a[i][j]=a[i][j]*-1;
 s=s+a[i][j];
 break;}

 printf("%ld\n",s=s+a[i][j]);

 return 0;
}