#include <iostream>
#include <vector>
#include <string>
#include <cmath>
#include <unordered_set>
#include <unordered_map>
#include <queue>
#include <algorithm>
#include <iomanip>
#include <cassert>
#include <functional>
#include <random>
#include <bitset>


using namespace std;
using ll = long long;
using ull = unsigned long long;
using ld = long double;
using pii = array<int,2>;
using pll = array<ll,2>;

#define vall(A) A.begin(), A.end()
#define vin(A) for (int iiii = 0, sz = A.size(); iiii < sz; iiii++){cin >> A[iiii];}
#define vout(A) for (int iiii = 0, sz = A.size(); iiii < sz; iiii++){cout << A[iiii] << " \n"[iiii == sz-1];}
#define vout2d(A) for (int iiii = 0, HHHH = A.size(), WWWW = (A.empty() ? 0 : A[0].size()); iiii < HHHH; iiii++){for (int jjjj = 0; jjjj < WWWW; jjjj++){cout << A[iiii][jjjj] << " \n"[jjjj==WWWW-1];}}
#define adjvin(A) for (int iiii = 1, sz = A.size(); iiii < sz; iiii++){cin >> A[iiii];}
#define adjvout(A) for (int iiii = 1, sz = A.size(); iiii < sz; iiii++){cout << A[iiii] << " \n"[iiii == sz-1];}
#define adjvout2d(A) for (int iiii = 1, HHHH = A.size(), WWWW = (A.empty() ? 0 : A[0].size()); iiii < HHHH; iiii++){for (int jjjj = 1; jjjj < WWWW; jjjj++){cout << A[iiii][jjjj] << " \n"[jjjj==WWWW-1];}}
#define btest(K,i) (((K)&(1ull<<(i))) != 0)
template<typename T> void print(T object){cout << (object) << "\n";}
template<typename T, typename U> void print(T object1, U object2){cout << (object1) << " " << (object2) << "\n";}
template<typename T, typename U, typename V> void print(T object1, U object2, V object3){cout << (object1) << " " << (object2) << " " << (object3) << "\n";}
vector<ull> pow2ll{1,2,4,8,16,32,64,128,256,512,1024,2048,4096,8192,16384,32768,65536,131072,262144,524288,1048576,2097152,4194304,8388608,16777216,33554432,67108864,134217728,268435456,536870912,1073741824,2147483648,4294967296,8589934592,17179869184,34359738368,68719476736,137438953472,274877906944,549755813888,1099511627776,2199023255552,4398046511104,8796093022208,17592186044416,35184372088832,70368744177664,140737488355328,281474976710656,562949953421312,1125899906842624,2251799813685248,4503599627370496,9007199254740992,18014398509481984,36028797018963968,72057594037927936,144115188075855872,288230376151711744,576460752303423488,1152921504606846976,2305843009213693952,4611686018427387904, 9223372036854775808ull};
vector<ull> pow10ll{1,10,100,1000,10000,100000,1000000,10000000,100000000,1000000000,10000000000,100000000000,1000000000000,10000000000000,100000000000000,1000000000000000,10000000000000000,100000000000000000,1000000000000000000, 10000000000000000000ull};
vector<ll> di{0,1,0,-1};
vector<ll> dj{1,0,-1,0};

void solve(){
    
    ll H,W;
    cin >> H >> W;

    vector<vector<string>> A(2*H+1, vector<string>(2*W+1, "."));

    for (ll i = 1; i <= H; i++){
        string T;
        cin >> T;
        for (ll j = 1; j <= W; j++){
            auto s = string{T[j-1]};
            if (s == "S" or s == "G"){
                s = ".";
            }
            A[2*i-1][2*j-1] = s;
        }
    }

    vector<vector<ll>> D(2*H+1, vector<ll>(2*W+1, -1));

    D[1][1] = 0;
    queue<pll> Q;
    Q.push({1,1});

    auto gridvalid = [](const ll &i, const ll &j, const ll &H, const ll &W){
        return i >= 0 && j >= 0 && i <= 2*H-1; j <= 2*W-1;
    };

    while (!Q.empty()){
        auto now = Q.front();
        Q.pop();
        vector<pll> adj{{0,1},{1,0},{0,-1},{-1,0}};
        if (now[0]%2){
            adj.push_back({2,0});
            adj.push_back({-2,0});
        }
        if (now[1]%2){
            adj.push_back({0,2});
            adj.push_back({0,-2});
        }

        for (auto& t : adj){
            if (gridvalid(now[0]+t[0], now[1]+t[1], H, W) && D[now[0]+t[0]][now[1]+t[1]] == -1 && A[now[0]+t[0]][now[1]+t[1]] == "."){
                D[now[0]+t[0]][now[1]+t[1]] = D[now[0]][now[1]]+1;
                Q.push({now[0]+t[0], now[1]+t[1]});
            }
        }
    }
    print(D[2*H-1][2*W-1]);
}



int main(){
    ios::sync_with_stdio(false);
    std::cin.tie(nullptr);

    ll T = 1;
    //cin >> T;
    while (T--){
        solve();
    }    
}