/Gặm cỏ

      #define _CRT_SECURE_NO_WARNINGS
        #include <iostream>
        #include <cstring>
        #include <queue>
        using namespace std;
        
        int n, m;
        
        int res = 0;
        char ch[100][100];
        bool mark[100][100]{ false };
        
        int dx[4]{ 0, 0, -1, 1 };
        int dy[4]{ -1, 1, 0, 0 };
        
        class Node {
        public:
          int x, y, t;
        
        public:
          Node(int x, int y, int t = 0) {
            this->x = x;
            this->y = y;
            this->t = t;
          }
        };
        
        void dfs(int x, int y) {
          queue<Node> iDex;
          iDex.push(Node(x, y));
        
          mark[x][y] = true;
        
          while (!iDex.empty()) {
            Node d = iDex.front();
            iDex.pop();
            if (d.x == 0 && d.y == 0) {
              res = max(res, d.t);
            }
            else {
              for (int i = 0; i < 4; i++) {
                int nextX = d.x + dx[i];
                int nextY = d.y + dy[i];
        
                if ((nextX >= 0 && nextX < n) && (nextY >= 0 && nextY < m)
                  && !mark[nextX][nextY] && (ch[nextX][nextY] == '.' || ch[nextX][nextY] == 'B')) {
                  iDex.push(Node(nextX, nextY, d.t + 1));
                  mark[nextX][nextY] = true;
                }
              }
            }
          }
        
        }
        
        int main() {
          cin >> n >> m;
        
        
          for (int i = 0; i < n; i++) {
            string s;
            cin >> s;
            strcpy(ch[i], s.c_str());
          }
        
          for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
              if (ch[i][j] == 'C') {
                dfs(i, j);
                cout << res << endl;
                return 0;
              }
            }
          }
        
          return 0;
        }