#include 
#include 
#include 
//#include 
using namespace std;
const int maxn = 1005;
const int INF = 1e9;
const int di[] = {-1, 1, 0, 0};
const int dj[] = {0, 0, -1, 1};
int n, m;
char mat[maxn][maxn];
int dist[maxn][maxn];
void paralel_bfs() {
    queue q;
    vector> v(n, vector(m, false));
    
    for(int i = 0; i < n; i++) {
        for(int j = 0; j < m; j++) {
            dist[i][j] = -1;
            if(mat[i][j] == 'G') {
                q.push(i);
                q.push(j);
                q.push(0);
                v[i][j] = true;
            }
        }
    }
    while(!q.empty()) {
        int ci = q.front(); q.pop();
        int cj = q.front(); q.pop();
        int cekor = q.front(); q.pop();
        
        if(mat[ci][cj] != 'G') {
            dist[ci][cj] = cekor;
        }
//        cout << ci << " " << cj << endl;
        for(int i = 0; i < 4; i++) {
            int ti = ci + di[i];
            int tj = cj + dj[i];
            if(ti >= 0 and ti < n and tj >= 0 and tj < m and dist[ti][tj] == -1 and mat[ti][tj] == '.' and !v[ti][tj]) {
                q.push(ti);
                q.push(tj);
                q.push(cekor + 1);
                v[ti][tj] = true;
            }
        }
    }
    
}
struct node {
    int ci, cj, d;
    node () {}
    node(int _ci, int _cj, int _d) {
        ci = _ci;
        cj = _cj;
        d = _d;
    }
    bool operator < (const node & tmp) const {
        return d < tmp.d;
    }
};
bool visited[maxn][maxn];
void dijkstra(int si, int sj, int ei, int ej) {
   
}
int main() {
    ios_base::sync_with_stdio(false);
//    ifstream cin("in.txt");
    cin >> n >> m;
    int si, sj, ei, ej;
    for(int i = 0; i < n; i++) {
        for(int j = 0; j < m; j++) {
            cin >> mat[i][j];
            if(mat[i][j] == 'R') {
                si = i;
                sj = j;
            }
            if(mat[i][j] == 'Z') {
                ei = i;
                ej = j;
            }
        }
    }
    mat[ei][ej] = '.';
    mat[si][sj] = '.';
//    cout << "DA" << endl;
    paralel_bfs();
//    cout << "DA" << endl;
    for(int i = 0; i < n; i++) {
        for(int j = 0; j < m; j++) {
            visited[i][j] = false;
        }
    }
    priority_queue pq;
    pq.push(node(si, sj, dist[si][sj]));
    int min_value = INF;
    while(!pq.empty()) {
        node c = pq.top();
        pq.pop();
        min_value = min(min_value, c.d);
        if(ei == c.ci and ej == c.cj) {
            cout << min_value << endl;
            break;
        }
        
//        cout << c.ci << "  " << c.cj << endl;
        for(int i = 0; i < 4; i++) {
            int ti = c.ci + di[i];
            int tj = c.cj + dj[i];
            if(ti >= 0 and ti < n and tj >= 0 and tj < m and !visited[ti][tj] and mat[ti][tj] == '.') {
                pq.push(node(ti, tj, dist[ti][tj]));
                visited[ti][tj] = true;
            }
        }
    }
    return 0;
}
/*
 .R234....
 ..1.3.1..
 ..G121G1.
 ....221..
 G...122..
 ....G12..
 ...**.3..
 ...Z..4..
 
 **/