INF = 10**9
dx = [-1,-1,-1, 0, 1, 1, 1, 0]
dy = [-1, 0, 1, 1, 1, 0,-1,-1]

def dfs(y,x):
    if x == n:
        if y > 0:
            for j in range(n):
                if a[y-1][j]:
                    return INF
        return dfs(y+1,0)
    elif y == m:
        for i in range(m):
            for j in range(n):
                if a[i][j]:
                    return INF
        return 0
    ret = INF
    if x == 0 or y == 0 or a[y-1][x-1]:
        a[y][x] ^= 1
        for i in range(8):
            ny = y + dy[i]
            nx = x + dx[i]
            if ny < 0 or ny >= m or nx < 0 or nx >= n: continue
            a[ny][nx] ^= 1
        ret = min(ret,dfs(y,x+1)+1)
        a[y][x] ^= 1
        for i in range(8):
            ny = y + dy[i]
            nx = x + dx[i]
            if ny < 0 or ny >= m or nx < 0 or nx >= n: continue
            a[ny][nx] ^= 1
    if x == 0 or y == 0 or not a[y-1][x-1]:
        ret = min(ret,dfs(y,x+1))
    return ret

m,n = map(int,input().split(' '))
a = [list(map(int,input().split(' '))) for i in range(m)]

print(dfs(0,0))