import java.util.Scanner;

public class Main {
    public static int n, m;
    public static int SUM;
    public static int[][] step = {{-1,0},{1,0},{0,-1},{0,1}};
    public static int[][] map;
    public static int[][] visited;
    public static int result = 10000;
    
    public void testDFS(int x, int y, int[][] v) {  //完成剪切后的另一部分是否是连通的
        v[x][y] = 2;
        for(int i = 0;i < 4;i++) {
            int x1 = x + step[i][0];
            int y1 = y + step[i][1];
            if(x1 < 0 || x1 >= n || y1 < 0 || y1 >= m)
                continue;
            if(v[x1][y1] == 0)
                testDFS(x1, y1, v);
        }
    }
    
    public void dfs(int startX, int startY, int count, int sum) {
        if(sum == SUM / 2) {
            int x = 0, y = 0, step = 0;
            int[][] v = new int[n][m];
            for(int i = 0;i < n;i++) {
                for(int j = 0;j < m;j++) {
                    if(visited[i][j] == 0) {
                        x = i;
                        y = j;
                    }    
                    v[i][j] = visited[i][j];
                }
            }
            testDFS(x, y, v);
            for(int i = 0;i < n;i++)
                for(int j = 0;j < m;j++)
                    if(v[i][j] == 2)
                        step++;
            if(step + count == n * m) {
                if(visited[0][0] == 1)
                    result = Math.min(result, count);
                else {
                    result = Math.min(result, step);
                }
            }
            return;
        } else if(sum > SUM / 2)
            return;
        for(int i = 0;i < 4;i++) {
            int x1 = startX + step[i][0];
            int y1 = startY + step[i][1];
            if(x1 < 0 || x1 >= n || y1 < 0 || y1 >= m)
                continue;
            if(visited[x1][y1] == 1)
                continue;
            visited[x1][y1] = 1;
            count++;
            sum += map[x1][y1];
            dfs(x1, y1, count, sum);
            sum -= map[x1][y1];
            count--;
            visited[x1][y1] = 0;
        }
    }
    
    public static void main(String[] args) {
        Main test = new Main();
        Scanner in = new Scanner(System.in);
        m = in.nextInt();
        n = in.nextInt();
        map = new int[n][m];
        SUM = 0;
        for(int i = 0;i < n;i++) {
            for(int j = 0;j < m;j++) {
                map[i][j] = in.nextInt();
                SUM += map[i][j];
            }
        }
        if(SUM % 2 == 0) {
            for(int i = 0;i < n;i++) {
                for(int j = 0;j < m;j++) {
                    visited = new int[n][m];
                    int sum = map[i][j];
                    int count = 1;
                    visited[i][j] = 1;
                    test.dfs(i, j, count, sum);
                }
            }
            if(result != 10000)
                System.out.println(result);
            else
                System.out.println("-1");
        } else
            System.out.println("-1");
    }
}