#include <cstdio>
#include <iostream>
#include <queue>
using namespace std;

char in;
int h,w,masu[504][504] = {};
struct joutai
{
	int x;
	int y;
	int nb;
	int nanho;
};

int check[504][504][2] = {};

queue<joutai> Q;
joutai saisho;
int goalx,goaly;
int ans = -1;
int ndx[8] = {1,2,2,1,-1,-2,-2,-1};
int ndy[8] = {-2,-1,1,2,2,1,-1,-2};
int bdx[4] = {1,1,-1,-1};
int bdy[4] = {-1,1,1,-1};

void nyuryoku()
{
	cin >> h >> w;
	for (int i = 2; i < h; i++)
	{
		for (int j = 2; j < w; j++)
		{
			cin >> in;
			if(in == 'S')
			{
				masu[i][j] = 1;
				saisho.x = i;
				saisho.y = j;
				saisho.nb = 1;
				saisho.nanho = 0;
			}
			else if(in == 'G')
			{
				masu[i][j] = 2;
				goalx = i;
				goaly = j;
			}
			else if(in == 'R')
			{
				masu[i][j] = 3;
			}
			else
			{
				masu[i][j] = 4;
			}
		}
	}
}

void keisan()
{
	Q.push(saisho);
	while(1)
	{
		if(Q.size() == 0)
		{
			break;
		}
		joutai miru = Q.front();
		Q.pop();	
		if(check[miru.x][miru.y][miru.nb] == 1)
		{
			continue;
		}
		check[miru.x][miru.y][miru.nb] = 1;
		joutai dainyu;
		if(miru.x == goalx && miru.y == goaly)
		{
			ans = miru.nanho;
			break;
		}
		if(miru.nb == 1)
		{
			for (int i = 0; i < 8; i++)
			{
				if(masu[miru.x + ndx[i]][miru.y + ndy[i]] == 4 ||
				masu[miru.x + ndx[i]][miru.y + ndy[i]] == 3||
				masu[miru.x + ndx[i]][miru.y + ndy[i]] == 2||
				masu[miru.x + ndx[i]][miru.y + ndy[i]] == 1)
				{
					if(masu[miru.x + ndx[i]][miru.y + ndy[i]] == 3)
					{
						dainyu.nb = 2;
					}
					else
					{
						dainyu.nb = 1;
					}
					dainyu.x = miru.x + ndx[i];
					dainyu.y = miru.y + ndy[i];
					dainyu.nanho = miru.nanho + 1;
					Q.push(dainyu);
				}
			}
		}
		else if(miru.nb == 2)
		{
			for (int i = 0; i < 4; i++)
			{
				if(masu[miru.x + bdx[i]][miru.y + bdy[i]] == 4 ||
				masu[miru.x + bdx[i]][miru.y + bdy[i]] == 3||
				masu[miru.x + bdx[i]][miru.y + bdy[i]] == 2||
				masu[miru.x + bdx[i]][miru.y + bdy[i]] == 1)
				{
					if(masu[miru.x + bdx[i]][miru.y + bdy[i]] == 3)
					{
						dainyu.nb = 1;
					}
					else
					{
						dainyu.nb = 2;
					}
					dainyu.x = miru.x + bdx[i];
					dainyu.y = miru.y + bdy[i];
					dainyu.nanho = miru.nanho + 1;
					Q.push(dainyu);
				}
			}
		}
	}
}

int main()
{
	nyuryoku();
	keisan();
	cout << ans << endl;
}