import sys
input = lambda :sys.stdin.readline()[:-1]
ni = lambda :int(input())
na = lambda :list(map(int,input().split()))
yes = lambda :print("yes");Yes = lambda :print("Yes");YES = lambda : print("YES")
no = lambda :print("no");No = lambda :print("No");NO = lambda : print("NO")
#######################################################################
c = 0
n,m = na()
s = [input() for i in range(n)]
a = s[0]
b = s[1]
z = []
x = m
y = m+1
ans = 1
for i in range(m):
    if a[i]!=b[i]:
        x = i
        z.append(b[i])
        break
    else:
        z.append(a[i])
for i in range(x+1, m):
    if a[i-1]!=b[i]:
        y = i
        z.append(a[i-1])
        break
    else:
        z.append(a[i-1])
if y == m + 1:
    z.append(a[-1])
for i in range(y, m+1):
    if a[i-1]!=b[i-1]:
        ans = 0
        z.append(a[i-1])
    else:
        z.append(a[i-1])
for i in range(2,n):
    for j in range(m):
        if s[i][j]!=z[j]:
            x = j
            break
    for j in range(x+1,m+1):
        if s[i][j-1]!=z[j]:
            ans = 0
if ans:
    c += 1
        
a,b = b,a
z = []
x = m
y = m+1
ans = 1
for i in range(m):
    if a[i]!=b[i]:
        x = i
        z.append(b[i])
        break
    else:
        z.append(a[i])
for i in range(x+1, m):
    if a[i-1]!=b[i]:
        y = i
        z.append(a[i-1])
        break
    else:
        z.append(a[i-1])
if y == m + 1:
    z.append(a[-1])
for i in range(y, m+1):
    if a[i-1]!=b[i-1]:
        ans = 0
        z.append(a[i-1])
    else:
        z.append(a[i-1])
for i in range(2,n):
    for j in range(m):
        if s[i][j]!=z[j]:
            x = j
            break
    for j in range(x+1,m+1):
        if s[i][j-1]!=z[j]:
            ans = 0
if ans:
    c += 1
print(c)