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; }

string COLOR(string s = "") { return "\x1b[" ~ s ~ "m"; }

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 M = readInt;
      const N = readInt;
      auto A = new string[M]; foreach (x; 0 .. M) A[x] = readToken;
      auto B = new string[M]; foreach (x; 0 .. M) B[x] = readToken;
      
      bool[2] can = [true, true];
      foreach (x; 0 .. M) foreach (y; 0 .. N) {
        can[0] = can[0] && (A[x][y] != B[x][y]);
        can[1] = can[1] && (A[x][y] != B[M - 1 - x][N - 1 - y]);
      }
      debug writeln(can);
      
      if (can[0] || can[1]) {
        real ans = 0.0L;
        real prob = 1.0L;
        real two = 1.0L;
        foreach (i; 0 .. 10^^3) {
          if (can[i & 1]) {
            ans += (prob * (1 - two)) * (i + 1);
            prob *= two;
          }
          two /= 2.0L;
        }
        writefln("%.20f", ans);
      } else {
        writeln("-1");
      }
    }
  } catch (EOFException e) {
  }
}