import std.conv, std.functional, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.complex, std.container, std.math, std.numeric, std.range, 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)); }


enum DX = [[+2, +1, -1, -2, -2, -1, +1, +2], [+1, -1, -1, +1]];
enum DY = [[+1, +2, +2, +1, -1, -2, -2, -1], [+1, +1, -1, -1]];

int H, W;
string[] S;

void main() {
  try {
    for (; ; ) {
      H = readInt();
      W = readInt();
      S = new string[H];
      foreach (x; 0 .. H) {
        S[x] = readToken();
      }
      
      auto q = DList!int();
      auto d = new int[][][](H, W, 2);
      foreach (x; 0 .. H) foreach (y; 0 .. W) {
        d[x][y][] = H * W * 2;
      }
      foreach (x; 0 .. H) foreach (y; 0 .. W) {
        if (S[x][y] == 'S') {
          d[x][y][0] = 0;
          q.insertBack(x);
          q.insertBack(y);
          q.insertBack(0);
        }
      }
      int ans = -1;
      for (; !q.empty; ) {
        const x = q.front; q.removeFront;
        const y = q.front; q.removeFront;
        const z = q.front; q.removeFront;
        const c = d[x][y][z];
        if (S[x][y] == 'G') {
          ans = c;
          break;
        }
        foreach (dir; 0 .. DX[z].length) {
          const xx = x + DX[z][dir];
          const yy = y + DY[z][dir];
          if (0 <= xx && xx < H && 0 <= yy && yy < W) {
            const zz = (S[xx][yy] == 'R') ? (z ^ 1) : z;
            if (chmin(d[xx][yy][zz], c + 1)) {
              q.insertBack(xx);
              q.insertBack(yy);
              q.insertBack(zz);
            }
          }
        }
      }
      writeln(ans);
    }
  } catch (EOFException e) {
  }
}