保证过

#include <bits/stdc++.h>
using namespace std;

const int MAXN = 50;
char mp[MAXN][MAXN];
int n, m;
int dir[4][2] = {{0, 1}, {1, 0}, {0, -1}, {-1, 0}};

bool in(int x, int y) {
return (x >= 1 && x <= n && y >= 1 && y <= m);
}

int BFS() {
queue<pair<int, int>> q;
q.push({1, 1});
mp[1][1] = '#'; // 标记起点已访问

int steps = 1;
while (!q.empty()) {
    int size = q.size();
    for (int k = 0; k < size; ++k) {
        int x = q.front().first, y = q.front().second;
        q.pop();

        if (x == n && y == m) {
            return steps;
        }

        for (int i = 0; i < 4; ++i) {
            int nx = x + dir[i][0], ny = y + dir[i][1];
            if (in(nx, ny) && mp[nx][ny] == '.') {
                q.push({nx, ny});
                mp[nx][ny] = '#'; // 标记已访问
            }
        }
    }
    ++steps;
}
return -1; // 理论上不会执行到这里

}

int main() {
cin >> n >> m;
for (int i = 1; i <= n; ++i) {
for (int j = 1; j <= m; ++j) {
cin >> mp[i][j];
}
}
int result = BFS();
cout << result << endl;
return 0;
}