import sys
input = sys.stdin.readline

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

base1 = []
base2 = []
s0,s1=S[0],S[1]
for i in range(M):
    s0i=s0[i]
    s1i=s1[i]
    if s0[i]==s1[i]:
        base1.append(s0i)
        base2.append(s0i)
    else:
        if i==M-1:
            base1.append(s0i)
            base1.append(s1i)
            base2.append(s1i)
            base2.append(s0i)
            break
        if s0[i+1]==s1[i+1]:
            base1.append(s0i)
            base1.append(s1i)
            base2.append(s1i)
            base2.append(s0i)
            for j in range(i+2,M):
                base1.append(s0[j])
                base2.append(s1[j])
        else:
            if s0[i+1]==s1i:
                base1.append(s0i)
                base1.append(s1i)
                base1.append(s1[i+1])
                for j in range(i+2,M):
                    base1.append(s1[j])
            if s1[i+1]==s0i:
                base2.append(s1i)
                base2.append(s0i)
                base2.append(s0[i+1])
                for j in range(i+2,M):
                    base2.append(s0[j])
        break
base1 = "".join(base1) if base1 is not None else None
base2 = "".join(base2) if base2 is not None else None

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 [base1,base2]:
    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)