#include <stdio.h>
#include <string.h>
#include <iostream>
#include <cmath>
#include <queue>
#define inf 100000000
using namespace std;char mp[30][30];struct Node{int x, y;
}st, ed, tool, temp, nxt;int vis[30][30];
double step[30][30];
int dir[4][2] = {1, 0, -1, 0, 0, 1, 0, -1};
int n, m;bool check(Node temp) {if (temp.x >= 0 && temp.x < n && temp.y >= 0 && temp.y < m && !vis[temp.x][temp.y] && mp[temp.x][temp.y] != 'X') {return true;)}return false;
}void get(Node temp, Node ed) {if (temp.x == ed.x) {int minn = min(temp.y, ed.y);int maxm = max(temp.y, ed.y);for (int i=minn+1; i<maxm; ++i) {if (mp[ed.x][i] == 'X' || mp[ed.x][i] == 'S') return;}int t = abs(temp.y - ed.y);step[ed.x][ed.y] = min(step[temp.x][temp.y]+t*0.2,step[ed.x][ed.y]);}else if (temp.y == ed.y) {int minn = min(temp.x, ed.x);int maxm = max(temp.x, ed.x);for (int i=minn+1; i<maxm; ++i) {if (mp[i][ed.y] == 'X' || mp[i][ed.x] == 'S') return;}int t = abs(temp.x - ed.x);step[ed.x][ed.y] = min(step[temp.x][temp.y]+t*0.2, step[ed.x][ed.y]);}
}void dfs(Node st, Node ed, bool v) {for (int i=0; i<4; ++i) {nxt.x = st.x + dir[i][0];nxt.y = st.y + dir[i][1];if (check(nxt)) {double t = step[st.x][st.y];if (v) t += 0.5;else t += 1;step[nxt.x][nxt.y] = min(step[nxt.x][nxt.y], t);vis[nxt.x][nxt.y] = 1;get(nxt, ed);if (nxt.x == tool.x && nxt.y == tool.y) dfs(nxt, ed, true);else dfs(nxt, ed, v);}}vis[st.x][st.y] = 0;return;
}int main() {while(~scanf("%d%d", &n, &m)) {bool v = false;memset(vis, 0, sizeof(vis));for (int i=0; i<n; ++i) {for (int j=0; j<m; ++j) {step[i][j] = inf;}}getchar();for (int i=0; i<n; ++i) {for (int j=0; j<m; ++j) {scanf("%c", &mp[i][j]);if (mp[i][j] == 'P') {st.x = i, st.y = j;}else if (mp[i][j] == 'B') {ed.x = i, ed.y = j;}else if (mp[i][j] == 'S') {tool.x = i, tool.y = j;}}if (i != n-1) scanf("\n");}step[st.x][st.y] = 0;vis[st.x][st.y] = 1;dfs(st, ed, v);get(st, ed);double ans = step[ed.x][ed.y];if (ans != inf)printf("%.1lf\n", ans);else printf("-1\n");}return 0;
}

/*
直接一个bfs，用两个数组保存有工具和没有工具时需要的时间。
*/#include <stdio.h>
#include <string.h>
#include <iostream>
#include <queue>
#define inf 1000000000
using namespace std;char mp[30][30];
int n, m;struct Node {int x, y, s; // 0 表示没有工具 1 表示有工具了。
}st, ed, temp, now, nxt;int step[30][30][2];int dir[4][2] = {1, 0, -1, 0, 0, 1, 0, -1};void bfs(Node st) {queue<Node> que;que.push(st);step[st.x][st.y][0] = 0;while(!que.empty()) {now = que.front();que.pop();if (now.x == ed.x) {int miny = min(now.y, ed.y);int maxy = max(now.y, ed.y);bool get = true;for (int y=miny+1; y<maxy; ++y) {if (mp[now.x][y] == 'X' || mp[now.x][y] == 'S') {get = false;break;}}if (get) step[ed.x][ed.y][now.s] = min(step[now.x][now.y][now.s] + 2 * (maxy - miny), step[ed.x][ed.y][now.s]);}if (now.y == ed.y) {int minx = min(now.x, ed.x);int maxx = max(now.x, ed.x);bool get = true;for (int x=minx+1; x<maxx; ++x) {if (mp[x][ed.y] == 'X' || mp[x][ed.y] == 'S') {get = false;}}if (get) step[ed.x][ed.y][now.s] = min(step[now.x][now.y][now.s]  + 2 * (maxx - minx), step[ed.x][ed.y][now.s]);}int T;for (int i=0; i<4; ++i) {nxt.x = now.x + dir[i][0];nxt.y = now.y + dir[i][1];nxt.s = now.s;if (nxt.x<0 || nxt.y<0 || nxt.x>=n || nxt.y>=m) continue;if (mp[nxt.x][nxt.y] == 'X') continue;if (now.s) T = 5;else T = 10;if (step[nxt.x][nxt.y][nxt.s] > step[now.x][now.y][now.s] + T) {step[nxt.x][nxt.y][nxt.s] = step[now.x][now.y][now.s] + T;if (mp[nxt.x][nxt.y] == 'S') {nxt.s = 1;step[nxt.x][nxt.y][1] = step[nxt.x][nxt.y][0];}que.push(nxt);}}}
}int main() {while(cin >> n >> m) {for (int i=0; i<n; ++i) {for (int j=0; j<m; ++j) {for (int k=0; k<2; ++k) {step[i][j][k] = inf;}}}for (int i=0; i<n; ++i) {for (int j=0; j<m; ++j) {cin >> mp[i][j];if (mp[i][j] == 'P') {st.x = i, st.y = j;}else if (mp[i][j] == 'B') {ed.x = i, ed.y = j;}}}st.s = 0;bfs(st);int ans = min(step[ed.x][ed.y][0], step[ed.x][ed.y][1]);if (ans == inf) cout << "-1\n";else printf("%.1lf\n", ans*1.0/10);}return 0;
}