// yukicoder: No.367 ナイトの転身
// bal4u 2019.8.20

#include <stdio.h>

//// 入出力関係
#if 1
#define gc() getchar_unlocked()
#else
#define gc() getchar()
#endif

int in() { // 非負整数の入力
	int n = 0, c = gc();
	do n = 10 * n + (c & 0xf); while ((c = gc()) >= '0');
	return n;
}

void ins(char *s) { // 文字列の入力　スペース以下の文字で入力終了
	do *s = gc();
	while (*s++ > ' ');
	*(s-1) = 0;
}

#define QMAX 500000
typedef struct { int r, c, t, knt; } Q;  // knt = knight
Q q[QMAX+5]; int top, end;
int H, W;
char map[505][505];
char vis[505][505][2];
int mk[8][2] = {{-1,-2},{-2, -1},{-2,1},{-1,2},{1,2},{2,1},{2,-1},{1,-2}};
int mb[4][2] = {{-1,-1},{-1,1},{1,1},{1,-1}};

int bfs(int sr, int sc, int gr, int gc) {
	int i, r, c, rr, cc, k, x, t;
	
	q[0].r = sr, q[0].c = sc, q[0].t = 0, q[0].knt = 1;
	top = 0, end = 1;
	while (top != end) {
		r = q[top].r, c = q[top].c, t = q[top].t, k = q[top].knt;
		if (++top == QMAX) top = 0;
		if (r == gr && c == gc) return t;
		if (vis[r][c][k]) continue;
		vis[r][c][k] = 1;
		if (k) {
			for (i = 0; i < 8; i++) {
				rr = r + mk[i][0], cc = c + mk[i][1];
				if (rr < 0 || rr >= H || cc < 0 || cc >= W) continue;
				x = k; if (map[rr][cc] == 'R') x = !k;
				if (vis[rr][cc][x]) continue;
				q[end].r = rr, q[end].c = cc, q[end].t = t+1, q[end].knt = x;
				if (++end == QMAX) end = 0;
			}
		} else {
			for (i = 0; i < 4; i++) {
				rr = r + mb[i][0], cc = c + mb[i][1];
				if (rr < 0 || rr >= H || cc < 0 || cc >= W) continue;
				x = k; if (map[rr][cc] == 'R') x = !k;
				if (vis[rr][cc][x]) continue;
				q[end].r = rr, q[end].c = cc, q[end].t = t+1, q[end].knt = x;
				if (++end == QMAX) end = 0;
			}
		}
	}
	return -1;
}
		
int main()
{
	int r, c, sr, sc, gr, gc;

	H = in(), W = in();
	for (r = 0; r < H; r++) {
		ins(map[r]);
		for (c = 0; c < W; c++) {
			if (map[r][c] == 'S') sr = r, sc = c;
			else if (map[r][c] == 'G') gr = r, gc = c;
		}
	}
	printf("%d\n", bfs(sr, sc, gr, gc));
	return 0;
}