import java.util.*; public class Main { public static void main(String[] args) { Scanner sc = new Scanner(System.in); String[] input = sc.nextLine().split(" "); int N = Integer.parseInt(input[0]); int M = Integer.parseInt(input[1]); char[][] map = new char[N][M]; int[][] escape = new int[N][M]; int[][] fire = new int[N][M]; boolean[][] fVisited = new boolean[N][M]; boolean[][] eVisited = new boolean[N][M]; Queue eQueue = new LinkedList<>(); Queue fQueue = new LinkedList<>(); List exits = new ArrayList<>(); for (int i = 0; i < N; i++) { map[i] = sc.nextLine().toCharArray(); for (int j = 0; j < M; j++) { if (map[i][j] == 'F') { fQueue.offer(new int[]{i, j}); fire[i][j] = 1; fVisited[i][j] = true; } if (map[i][j] == 'J') { eQueue.offer(new int[]{i, j}); escape[i][j] = 1; eVisited[i][j] = true; } if ((map[i][j]=='.' || map[i][j]=='J') && (i==0 || j==0 || i==N-1 || j==M-1)) { exits.add(new int[]{i, j}); } } } int[] current, dx = {-1, 0, 1, 0}, dy = {0, -1, 0, 1}; int y, x, ny, nx; while (!fQueue.isEmpty()) { current = fQueue.poll(); y = current[0]; x = current[1]; for (int i = 0; i < 4; i++) { ny = y + dy[i]; nx = x + dx[i]; if (0 <= ny && ny < N && 0 <= nx && nx < M && !fVisited[ny][nx] && map[ny][nx] != '#') { fQueue.offer(new int[]{ny, nx}); fVisited[ny][nx] = true; fire[ny][nx] = fire[y][x] + 1; } } } while (!eQueue.isEmpty()) { current = eQueue.poll(); y = current[0]; x = current[1]; for (int i = 0; i < 4; i++) { ny = y + dy[i]; nx = x + dx[i]; if (0 <= ny && ny < N && 0 <= nx && nx < M && !eVisited[ny][nx] && map[ny][nx] != '#' && map[ny][nx] != 'F') { if (fire[ny][nx] > escape[y][x]+1) { escape[ny][nx] = escape[y][x] + 1; eQueue.offer(new int[]{ny, nx}); eVisited[ny][nx] = true; } } } } int answer = 0; for (int[] pos : exits) { answer = Math.max(answer, escape[pos[0]][pos[1]]); } if (answer == 0) { System.out.println("IMPOSSIBLE"); } else { System.out.println(answer); } } }

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