#include <iostream>
#include <vector>
using namespace std;
int r,c,maxi=-1e9,x1,x2,y1,y2;
int main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cin >> r >> c;
int arr[r+1][c+1];
int prearr[r+1][c+1];
for(int j=1;j<=c;j++){
prearr[0][j] = 0;
}
for(int i=1;i<=r;i++){
for(int j=1;j<=c;j++){
cin >> arr[i][j];
if(arr[i][j]==0){
arr[i][j] = -1;
}
prearr[i][j] = prearr[i-1][j]+arr[i][j];
}
}
for(int i=1;i<=r;i++){
for(int j=i;j<=r;j++){
int mini=0,totsum=0,pos=-1;
for(int k=1;k<=c;k++){
totsum += prearr[j][k]-prearr[i-1][k];
if(totsum-mini>maxi){
maxi = totsum-mini;
x1 = i;
x2 = j;
y1 = pos+1;
y2 = k;
}
if(totsum<mini){
mini = totsum;
pos = k;
}
}
}
}
int cnt=0;
for(int i=1;i<=r;i++){
for(int j=1;j<=c;j++){
if(i>=x1 and i<=x2 and j>=y1 and j<=y2){
if(arr[i][j]==-1){
cnt++;
}
}
else{
if(arr[i][j]==1){
cnt++;
}
}
}
}
cout << cnt;
return 0;
}
