#include <bits/stdc++.h>
using namespace std;
using ll = long long;
int main() {
ios_base::sync_with_stdio(false);cin.tie(0);
ll N,M;
ll ones = 0;
ll sum = 0;
cin>>N>>M;
ll A[N + 1][M + 1];
for(ll i = 1;i <= N;i++){
for(ll j = 1;j <= M;j++){
ll a;
cin>>a;
if(a == 0){
A[i][j] = -1;
}else{
A[i][j] = 1;
ones += 1;
}
}
}
ll ss[N + 1][M + 1];
ll column[M + 1];
ll arr[M + 1];
memset(ss,0,sizeof(ss));
memset(column,0,sizeof(column));
memset(arr,0,sizeof(arr));
for(ll i = 1;i <= N;i++){
for(ll j = 1;j <= M;j++){
ss[i][j] = ss[i - 1][j] + A[i][j];
}
}
for(ll x1 = 1;x1 <= N;x1++){
for(ll x2 = x1;x2 <= N;x2++){
for(ll width = 1;width <= M;width++){
arr[width] = ss[x2][width] - ss[x1 - 1][width];
}
for(ll width = 1;width <= M;width++){
column[width] = max(column[width - 1] + arr[width],arr[width]);
sum = max(sum,column[width]);
}
}
}
cout<<ones - sum<<'\n';
}
