#include<iostream>
#include<queue>
#include<cstring>
using namespace std;
const int BUF = 505;


class Data {
public:
    bool type;
    int r, c;
    Data(){}
    Data(bool type, int r, int c):
        type(type), r(r), c(c){}
};


int row, col;
int bgnR, bgnC;
int endR, endC;
bool isRed[BUF][BUF];


void read() {
    memset(isRed, 0, sizeof(isRed));
    
    cin >> row >> col;
    for (int i = 0; i < row; ++i) {
        for (int j = 0; j < col; ++j) {
            char ch;
            cin >> ch;
            isRed[i][j] = ch == 'R';

            if (ch == 'S') {
                bgnR = i;
                bgnC = j;
            }
            if (ch == 'G') {
                endR = i;
                endC = j;
            }
        }
    }
}


void work() {
    queue<Data> Q;
    int cost[2][BUF][BUF];
    
    memset(cost, -1, sizeof(cost));
    Q.push(Data(0, bgnR, bgnC));
    cost[0][bgnR][bgnC] = 0;

    
    while (!Q.empty()) {
        Data curr = Q.front();
        Q.pop();
        
        if (curr.r == endR && curr.c == endC) {
            cout << cost[curr.type][curr.r][curr.c] << endl;
            return;
        }
        
        // knight の動き
        static int kdr[] = {-2, -1,  1,  2,  2,  1, -1, -2};
        static int kdc[] = { 1,  2,  2,  1, -1, -2, -2, -1};
        
        // mini bishop の動き
        static int bdr[] = {-1, 1,  1, -1};
        static int bdc[] = { 1, 1, -1, -1};

        for (int i = 0; i < (curr.type == 0 ? 8 : 4); ++i) {
            int nr = curr.r + (curr.type == 0 ? kdr[i] : bdr[i]);
            int nc = curr.c + (curr.type == 0 ? kdc[i] : bdc[i]);
            
            if (!(0 <= nr && nr < row && 0 <= nc && nc < col)) continue;

            bool nType = isRed[nr][nc] ? !curr.type : curr.type;

            if (cost[nType][nr][nc] == -1) {
                cost[nType][nr][nc] = cost[curr.type][curr.r][curr.c] + 1;
                Q.push(Data(nType, nr, nc));
            }
        }
    }

    cout << -1 << endl;
}


int main() {
    read();
    work();
    return 0;
}