import sys
input = sys.stdin.readline

N,M=map(int,input().split())
S=[input().strip() for _ in range(N)]

base = []
s0,s1=S[0],S[1]
for i in range(M):
    s0i=s0[i]
    s1i=s1[i]
    if s0[i]!=s1[i]:
        if i==M-1:
            base.append(s0[:-1]+s0i+s1i)
            base.append(s0[:-1]+s1i+s0i)
            break
        if s0[i+1]==s1[i+1]:
            base.append(s0[:i]+s0i+s1i+s0[i+1:])
            base.append(s0[:i]+s1i+s0i+s0[i+1:])
        if s0[i+1]==s1i:
            base.append(s0[:i+1]+s1[i:])

        if s1[i+1]==s0i:
            base.append(s1[:i+1]+s0[i:])
        break

def judge(s,b):
    j=0
    for i,ss in enumerate(s):
        if ss!=b[j]:
            j+=1
            if j>=len(b) or ss!=b[j]:
                return False
            if j>i+1:return False
        j+=1
    return j<=len(b)

ans=0
for b in set(base):
    if b is None:continue
    if len(b)!=M+1:continue
    for s in S:
        if judge(s,b):continue
        break
    else:
        ans+=1
print(ans)