import sys

# sys.setrecursionlimit(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 << 63)-1
# inf = (1 << 31)-1
md = 10**9+7
# md = 998244353

def compare(s, t):
    a = b = 0
    res = ""
    for i in range(m-1):
        if s[i+a] != t[i+b]:
            if a == 0 and s[i+1] == t[i]:
                res += s[i]
                a = 1
            elif a == 1 and b == 0 and (s[i+1] == t[i+1] or i+1 == m):
                res += t[i]
                b = 1
            else:
                return ""
        res += s[i+a]
    return res

def check(t):
    if not t: return False
    for s in ss[2:]:
        if ng(s, t): return False
    return True

def ng(s, t):
    t = iter(t)
    for c in s:
        if c not in t: return True
    return False

n, m = LI()
ss = [SI() for _ in range(n)]
tt = set()
t = compare(ss[0], ss[1])
if check(t): tt.add(t)
t = compare(ss[1], ss[0])
if check(t): tt.add(t)
print(len(tt))