A = []
x = input()
while x != "exit":
    if x == "pop":
        if len(A) == 0:
            print("error")
        else:        
            print(A[0])
            A.pop(0)
            
    if x == "front":
        if len(A) == 0:
            print("error")
        else:    
            print(A[0])
            
    if x == "size":
        print(len(A))
        
    if x == "clear":
        A = []
        print("ok")   
        
    x = x.split()
    
    if x[0] == "push":
        A.append(int(x[1]))
        print("ok")    
        
    x = input()
    

print("bye")



def bfs(z):
    A = [-1 for i in range(0, len(a) + 1)]
    B = [True for i in range(0, len(a) + 1)]
    A[z] = 0
    B[z] = False
    q = [z]
    while q:
        t = q.pop(0)
        x = a[t]
        for j in x:
            if B[j]:
                B[j] = False
                A[j] = A[t] + 1
                q.append(j)
    return A    
        
n, m =map(int, input(). split())
x1, y1 = map(int, input(). split())
x1 -= 1
y1 -= 1
x2, y2 = map(int, input(). split())
x2 -= 1
y2 -= 1 
A = []
for i in range(n):
    A.append(input())
a = dict()
for i in range(0, n * m):
    a[i] = set()
for i in range(n):
    for j in range(m):
        if i < n - 1:
            if A[i + 1][j] == ".":
                a[i * m + j].add((i + 1) * m + j)
        if j < m - 1:
            if A[i][j + 1] == ".":
                a[i * m + j].add((i) * m + j + 1)
        if i > 0:
            if A[i - 1][j] == ".":
                a[i * m + j].add((i - 1) * m + j)
        if j > 0:
            if A[i][j - 1] == ".":
                a[i * m + j].add((i) * m + j - 1)
z = (bfs(x1 * m + y1)[x2 * m + y2])
print(z)