#include<bits/stdc++.h>
#define Add(x,y) (x+y>=mod)?(x+y-mod):(x+y)
#define lowbit(x) x&(-x)
#define pi pair<ll,ll>
#define pii pair<ll,pair<ll,ll>>
#define iip pair<pair<ll,ll>,ll>
#define ppii pair<pair<ll,ll>,pair<ll,ll>>
#define fi first
#define se second
#define full(l,r,x) for(auto it=l;it!=r;it++) (*it)=x
#define Full(a) memset(a,0,sizeof(a))
#define open(s1,s2) freopen(s1,"r",stdin),freopen(s2,"w",stdout);
#define For(i,l,r) for(int i=l;i<=r;i++)
#define _For(i,l,r) for(int i=r;i>=l;i--)
using namespace std;
typedef double db;
typedef unsigned long long ull;
typedef int ll;
bool Begin;
const ll N=505;
inline ll read(){
    ll x=0,f=1;
    char c=getchar();
    while(c<'0'||c>'9'){
        if(c=='-')
          f=-1;
        c=getchar();
    }
    while(c>='0'&&c<='9'){
        x=(x<<1)+(x<<3)+(c^48);
        c=getchar();
    }
    return x*f;
}
inline void write(ll x){
	if(x<0){
		putchar('-');
		x=-x;
	}
	if(x>9)
	  write(x/10);
	putchar(x%10+'0');
}
inline char get(){
    char c;
    while(1){
        c=getchar();
        if(c=='S'||c=='G'||c=='R'||c=='.')
          break;
    }
    return c;
}
struct Node{
    ll x,y;
    bool F;
};
char c;
ll n,m,sx,sy,tx,ty,ans;
ll dx1[]={1,1,2,2,-1,-1,-2,-2},dy1[]={-2,2,-1,1,-2,2,-1,1};
ll dx2[]={1,-1,1,-1},dy2[]={-1,1,1,-1};
ll dis[N][N][2];
bool f[N][N];
queue<Node> Q;
void bfs(){
    dis[sx][sy][0]=0;
    Q.push({sx,sy,0});
    while(!Q.empty()){
        ll x=Q.front().x,y=Q.front().y;
        bool F=Q.front().F,nF;
        Q.pop();
        if(F){
            for(int i=0;i<4;i++){
                ll zx=x+dx2[i],zy=y+dy2[i];
                if(zx<1||zx>n||zy<1||zy>m)
                  continue;
                if(f[zx][zy])
                  nF=F^1ll;
                else
                  nF=F;
                if(dis[zx][zy][nF]>dis[x][y][F]+1){
                    dis[zx][zy][nF]=dis[x][y][F]+1;
                    Q.push({zx,zy,nF});
                }
            }
        }
        else{
            for(int i=0;i<8;i++){
                ll zx=x+dx1[i],zy=y+dy1[i];
                if(zx<1||zx>n||zy<1||zy>m)
                  continue;
                if(f[zx][zy])
                  nF=F^1ll;
                else
                  nF=F;
                if(dis[zx][zy][nF]>dis[x][y][F]+1){
                    dis[zx][zy][nF]=dis[x][y][F]+1;
                    Q.push({zx,zy,nF});
                }
            }
        }
    }
}
bool End;
int main(){
    n=read(),m=read();
    for(int i=1;i<=n;i++){
        for(int j=1;j<=m;j++){
            char c=get();
            if(c=='S')
              sx=i,sy=j;
            else if(c=='G')
              tx=i,ty=j;
            else if(c=='R')
              f[i][j]=1;
            dis[i][j][0]=dis[i][j][1]=1e9;
        }
    }
    bfs();
    ans=min(dis[tx][ty][0],dis[tx][ty][1]);
    write(ans==1e9?-1:ans);
	//cerr<<'\n'<<abs(&Begin-&End)/1048576<<"MB";
	return 0;
}