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) { } }