#define _CRT_SECURE_NO_WARNINGS
#define _USE_MATH_DEFINES

#include <bits/stdc++.h>
using namespace std;
using i8  = int8_t;  using u8  = uint8_t;
using i16 = int16_t; using u16 = uint16_t;
using i32 = int32_t; using u32 = uint32_t;
using i64 = int64_t; using u64 = uint64_t;
using f32 = float_t; using f64 = double_t;
using usize = size_t;using str = string;
template <class T> using vec = vector<T>;
#define times(n, i) for (i32 i = 0; i < (n); i++)
#define range(n, m, i) for (i32 i = (n); i < (m); i++)
#define upto(n, m, i) for (i32 i = (n); i <= (m); i++)
#define downto(n, m, i) for (i32 i = (n); i >= (m); i--)
#define foreach(xs, x) for (auto &x : (xs))
#define all(xs) (xs).begin(), (xs).end()
#define sortall(xs) sort(all(xs))
#define reverseall(xs) reverse(all(xs))
#define uniqueall(xs) (xs).erase(unique(all(xs)), (xs).end())
#define maximum(xs) *max_element(all(xs))
#define minimum(xs) *min_element(all(xs))
const i64 MOD = 1000000007;

vec<str> m;
vec<vec<i32>> fp[2];
i32 sx, sy, gx, gy;

i32 knight_x[8] = { -2, -1, 1, 2, 2, 1, -1, -2 };
i32 knight_y[8] = { -1, -2, -2, -1, 1, 2, 2, 1 };
i32 bishop_x[4] = { -1, 1, 1, -1 };
i32 bishop_y[4] = { -1, -1, 1, 1 };

i32 main()
{
    i32 h, w;
    cin >> h >> w;
    m.resize(h); fp[0].resize(h); fp[1].resize(h);
    times(h, i) {
        cin >> m[i];
        fp[0][i].resize(w);
        fp[1][i].resize(w);
        times(w, j) {
            if (m[i][j] == 'S') {
                sx = j; sy = i;
            } else if (m[i][j] == 'G') {
                gx = j; gy = i;
            }
            fp[0][i][j] = -1;
            fp[1][i][j] = -1;
        }
    }
    i32 last_t = 0;
    set<tuple<i32, i32, i32, i32>> rest;
    rest.insert(make_tuple(0, sx, sy, 0));
    while (rest.size()) {
        i32 turn = get<0>(*rest.begin());
        i32 x = get<1>(*rest.begin());
        i32 y = get<2>(*rest.begin());
        i32 t = get<3>(*rest.begin());
        rest.erase(rest.begin());
        if (fp[t][y][x] > -1)
            continue;
        fp[t][y][x] = turn;
        if (x == gx && y == gy) {
            last_t = t;
            break;
        }
        if (m[y][x]  == 'R')
            t ^= 1;
        if (t == 0) {
            times(8, i) {
                i32 nx = x + knight_x[i];
                i32 ny = y + knight_y[i];
                if (0 <= nx && nx < w && 0 <= ny && ny < h) {
                    rest.insert(make_tuple(turn+1, nx, ny, t));
                }
            }
        } else {
            times(4, i) {
                i32 nx = x + bishop_x[i];
                i32 ny = y + bishop_y[i];
                if (0 <= nx && nx < w && 0 <= ny && ny < h) {
                    rest.insert(make_tuple(turn+1, nx, ny, t));
                }
            }
        }
    }

    cout << fp[last_t][gy][gx] << endl;
    return 0;
}