#include <iostream>
#include <queue>
#include <list>
using namespace std;
#define N 0
#define B 1
#define MAX 250000
#define ull unsigned long long int

int q[MAX][4];
int head = 0, tail = 0;

int h, w, x, y;
int state = N;
bool*** f;
int c = 1;

void pushQ(int x, int y, int c, int s) {
	q[tail][0] = x;
	q[tail][1] = y;
	q[tail][2] = c;
	q[tail][3] = s;
	++tail;
	if (tail >= MAX) {
		tail = 0;
	}
}

void pushqueue() {
	if (state) { // state = B
		if (x - 1 >= 0) {
			if (y - 1 >= 0) {
				if (!f[y-1][x-1][state]) {
					pushQ(x - 1, y - 1, c, state);
				}
			}
			if (y + 1 < h) {
				if (!f[y+1][x-1][state]) {
					pushQ(x - 1, y + 1, c, state);
				}
			}
		}
		if (x + 1 < w) {
			if (y - 1 >= 0) {
				if (!f[y-1][x+1][state]) {
					pushQ(x + 1, y - 1, c, state);
				}
			}
			if (y + 1 < h) {
				if (!f[y+1][x+1][state]) {
					pushQ(x + 1, y + 1, c, state);
				}
			}
		}
	}
	else { // state = N
		if (x - 2 >= 0) {
			if (y - 1 >= 0) {
				if (!f[y-1][x-2][state]) {
					pushQ(x - 2, y - 1, c, state);
				}
			}
			if (y + 1 < h) {
				if (!f[y+1][x-2][state]) {
					pushQ(x - 2, y + 1, c, state);
				}
			}
		}
		if (x - 1 >= 0) {
			if (y - 2 >= 0) {
				if (!f[y-2][x-1][state]) {
					pushQ(x - 1, y - 2, c, state);
				}
			}
			if (y + 2 < h) {
				if (!f[y+2][x-1][state]) {
					pushQ(x - 1, y + 2, c, state);
				}
			}
		}
		if (x + 1 < w) {
			if (y - 2 >= 0) {
				if (!f[y-2][x+1][state]) {
					pushQ(x + 1, y - 2, c, state);
				}
			}
			if (y + 2 < h) {
				if (!f[y+2][x+1][state]) {
					pushQ(x + 1, y + 2, c, state);
				}
			}
		}
		if (x + 2 < w) {
			if (y - 1 >= 0) {
				if (!f[y-1][x+2][state]) {
					pushQ(x + 2, y - 1, c, state);
				}
			}
			if (y + 1 < h) {
				if (!f[y+1][x+2][state]) {
					pushQ(x + 2, y + 1, c, state);
				}
			}
		}
	}
}

void popq() {
	x = q[head][0];
	y = q[head][1];
	c = q[head][2];
	state = q[head][3];
	++head;
	if (head >= MAX) {
		head = 0;
	}
}

int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);
	cin >> h >> w;
	char** d = new char*[h];
	f = new bool**[h];
	for (int i = 0; i < h; ++i) {
		d[i] = new char[w];
		f[i] = new bool*[w];
		for (int j = 0; j < w; ++j) {
			cin >> d[i][j];
			f[i][j] = new bool[2];
			if (d[i][j] == 'S') {
				d[i][j] = '.';
				f[i][j][N] = true;
				f[i][j][B] = false;
				y = i;
				x = j;
			}
			else {
				f[i][j][N] = false;
				f[i][j][B] = false;
			}
		}
	}

	pushqueue();
	while (head != tail) {
		popq();
		f[y][x][state] = true;
		if (d[y][x] == 'G') {
			cout << c << endl;
			goto end;
		}
		else if (d[y][x] == 'R') {
			state ^= 1; // stateが1なら0、0なら1
		}
		++c;
		pushqueue();
	}
	cout << -1 << endl;
end:
	return 0;
}