import std.conv, std.functional, std.range, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.bitmanip, std.complex, std.container, std.math, std.mathspecial, std.numeric, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken.to!int; }
long readLong() { return readToken.to!long; }
real readReal() { return readToken.to!real; }

bool chmin(T)(ref T t, in T f) { if (t > f) { t = f; return true; } else { return false; } }
bool chmax(T)(ref T t, in T f) { if (t < f) { t = f; return true; } else { return false; } }

int binarySearch(alias pred, T)(in T[] as) { int lo = -1, hi = cast(int)(as.length); for (; lo + 1 < hi; ) { const mid = (lo + hi) >> 1; (unaryFun!pred(as[mid]) ? hi : lo) = mid; } return hi; }
int lowerBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a >= val)); }
int upperBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a > val)); }




void main() {
  try {
    for (; ; ) {
      const N = readInt;
      const M = readInt;
      auto S = new string[N];
      foreach (i; 0 .. N) {
        S[i] = readToken;
      }
      
      bool check(string t) {
        debug {
          writeln("check ", t);
        }
        foreach (i; 0 .. N) {
          foreach (j; 0 .. M + 1) {
            if (j == M || S[i][j] != t[j]) {
              if (S[i][j .. M] != t[j + 1 .. M + 1]) {
                return false;
              }
            }
          }
        }
        return true;
      }
      
      int ans;
      foreach (x; 0 .. M) if (S[0][x] != S[1][x]) {
        foreach (h; 0 .. 2) {
          if (check(S[h][0 .. x] ~ S[h ^ 1][x] ~ S[h][x .. M])) {
            ++ans;
          }
        }
        break;
      }
      writeln(ans);
    }
  } catch (EOFException e) {
  }
}