import sys

# sys.setrecursionlimit(200005)
# sys.set_int_max_str_digits(200005)
int1 = lambda x: int(x)-1
pDB = lambda *x: print(*x, end="\n", file=sys.stderr)
p2D = lambda x: print(*x, sep="\n", end="\n\n", file=sys.stderr)
def II(): return int(sys.stdin.readline())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def SI(): return sys.stdin.readline().rstrip()

dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
# inf = -1-(-1 << 31)
inf = -1-(-1 << 62)

# md = 10**9+7
md = 998244353

# s=1
# ans=0
# for i in range(1,100):
#     p=1-1/pow(2,i-1)
#     ans+=s*p*i
#     s*=(1-p)
#     print(ans)

h,w=LI()
s=[SI() for _ in range(h)]
t=[SI() for _ in range(h)]

rev=0
for i in range(h):
    for j in range(w):
        if s[i][j]==t[i][j]:
            rev=1
            break
    if rev:break

for i in range(h):
    for j in range(w):
        if s[i][j] == t[h-1-i][w-1-j]:
            rev|=2

if rev==3:
    print(-1)
elif rev==2:
    print(3.128936827211877)
elif rev==1:
    print(3.5317401904617327)
else:
    print(2.641632560655154)