import java.io.*;
import java.util.*;
public class orchard {
public static void main(String[] args) throws IOException {
Scanner sc = new Scanner();
PrintWriter out = new PrintWriter(System.out);
int n = sc.nextInt(), m = sc.nextInt();
int[][] a = new int[n][m], prefix = new int[n][m];
int ones = 0;
for (int i = 0; i < n; i++)
for (int j = 0; j < m; j++) {
a[i][j] = sc.nextInt();
if (a[i][j] == 0)
a[i][j] = -1;
else
ones++;
prefix[i][j] = a[i][j];
if (i > 0)
prefix[i][j] += prefix[i - 1][j];
if (j > 0)
prefix[i][j] += prefix[i][j - 1];
if (i > 0 && j > 0)
prefix[i][j] -= prefix[i - 1][j - 1];
}
int ans = 0;
for (int u = 0; u < n; u++) {
for (int d = u; d < n; d++) {
int min = 0;
for (int j = 0; j < m; j++) {
int sum = prefix[d][j];
if (u > 0) {
sum -= prefix[u - 1][j];
}
ans = Math.max(sum - min, ans);
min = Math.min(min, sum);
}
}
}
out.println(ones - ans);
out.close();
}
static class Scanner {
BufferedReader br;
StringTokenizer st;
Scanner() {
br = new BufferedReader(new InputStreamReader(System.in));
}
Scanner(String fileName) throws FileNotFoundException {
br = new BufferedReader(new FileReader(fileName));
}
String next() throws IOException {
while (st == null || !st.hasMoreTokens())
st = new StringTokenizer(br.readLine());
return st.nextToken();
}
String nextLine() throws IOException {
return br.readLine();
}
int nextInt() throws IOException {
return Integer.parseInt(next());
}
long nextLong() throws NumberFormatException, IOException {
return Long.parseLong(next());
}
double nextDouble() throws NumberFormatException, IOException {
return Double.parseDouble(next());
}
boolean ready() throws IOException {
return br.ready();
}
}
}
