#include <stdio.h>

int h, w;
char str[500][501];
int dp[2][500][500];

#define MAX 500 * 500 * 2

int queue_i[MAX];
int queue_j[MAX];
int queue_v[MAX]; // step (+1)
int queue_s[MAX]; // knight : 0, bishop : 1
int set, get;

int next_i[2][8] = { { -2, -2, -1, -1, +1, +1, +2, +2 }, { -1, -1, +1, +1 } };
int next_j[2][8] = { { -1, +1, -2, +2, -2, +2, -1, +1 }, { -1, +1, -1, +1 } };
int next_n[2] = { 8, 4 };

int in(int i, int j) {
	return 0 <= i && i < h && 0 <= j && j < w;
}

int main() {
	scanf("%d%d", &h, &w);
	for(int i = 0; i < h; i++) { scanf("%s", str[i]); }
	
	int s_i, s_j, g_i, g_j;
	for(int i = 0; i < h; i++) {
	for(int j = 0; j < w; j++) {
		if(str[i][j] == 'S') { s_i = i; s_j = j; }
		if(str[i][j] == 'G') { g_i = i; g_j = j; }
	}
	}
	
	dp[2][s_i][s_j] = 1;
	queue_i[set] = s_i;
	queue_j[set] = s_j;
	queue_v[set] = 1;
	queue_s[set] = 0;
	set++;
	
	while(get != set) {
		int i, j, v, s;
		i = queue_i[get];
		j = queue_j[get];
		v = queue_v[get];
		s = queue_s[get];
		
		if(str[i][j] == 'R') { s = (! s); }
		
		for(int k = 0; k < next_n[s]; k++) {
			int ii = i + next_i[s][k];
			int jj = j + next_j[s][k];
			if( in(ii, jj) && dp[s][ii][jj] == 0 ) {
				dp[s][ii][jj] = v + 1;
				queue_i[set] = ii;
				queue_j[set] = jj;
				queue_v[set] = v + 1;
				queue_s[set] = s;
				set++;
			}
		}
		
		get++;
	}
	
	int ans;
	int k = dp[0][g_i][g_j];
	int b = dp[1][g_i][g_j];
	if( k == 0 || b == 0 ) {
		ans = k < b ? b : k;
	} else {
		ans = k < b ? k : b;
	}
	
	printf("%d\n", ans - 1);
	
	return 0;
}