import java.io.*; import java.util.*; public class Main { static int[] head; static int[] to; static int[] next; static int[] black; static int INF; public static void main(String[] args) throws IOException { PrintWriter out = new PrintWriter(System.out); FastScanner fs = new FastScanner(); int N = fs.nextInt(); head = new int[N + 1]; to = new int[N* 2]; black = new int[N + 1]; next = new int[N * 2]; Arrays.fill(head, -1); INF = N + 1; for(int i = 0; i < N - 1; i++) { int u = fs.nextInt(), v = fs.nextInt(); addEdge(i, u, v); addEdge(N + i, v, u); } for(int i = 1; i <= N; i++) { black[i] = fs.nextInt(); } boolean[] visited = new boolean[N + 1]; visited[1] = true; int[][][] dp = new int[N + 1][2][2]; dp(1, visited, dp); int min = Math.min(dp[1][0][0], dp[1][0][1]); if(min >= INF) { out.print("impossible"); }else { out.print(min); } out.flush(); } private static void dp(int curr, boolean[] visited, int[][][] dp) { dp[curr][0][0] = black[curr] == 1 ? INF : 0; dp[curr][0][1] = black[curr] == 1 ? 1 : INF; dp[curr][1][0] = black[curr] == 1 ? 0 : INF; dp[curr][1][1] = black[curr] == 1 ? INF : 1; for(int e = head[curr]; e != -1; e = next[e]) { int node = to[e]; if(!visited[node]) { visited[node] = true; dp(node, visited, dp); int[][] temp = new int[2][2]; temp[0][0] = Math.min(dp[curr][0][0] + dp[node][0][0], dp[curr][1][0] + dp[node][0][1]); temp[0][1] = Math.min(dp[curr][0][1] + dp[node][1][0], dp[curr][1][1] + dp[node][1][1]); temp[1][0] = Math.min(dp[curr][1][0] + dp[node][0][0], dp[curr][0][0] + dp[node][0][1]); temp[1][1] = Math.min(dp[curr][1][1] + dp[node][1][0], dp[curr][0][1] + dp[node][1][1]); for(int i = 0; i < 2; i++) { for(int j = 0; j < 2; j++) { dp[curr][i][j] = temp[i][j]; } } } } } private static void addEdge(int e, int u, int v) { next[e] = head[u]; head[u] = e; to[e] = v; } static class FastScanner { InputStream is = System.in; byte[] buffer = new byte[1 << 17]; int pointer = 0; int bufferLength = 0; private byte readByte() { if (pointer == bufferLength) { try { bufferLength = is.read(buffer); pointer = 0; if (bufferLength == -1) bufferLength = 0; } catch (IOException e) { throw new RuntimeException(e); } } return bufferLength == 0 ? -1 : buffer[pointer++]; } private void skip() { int b; while ((b = readByte()) != -1 && b <= 32) ; if (b != -1) pointer--; } public int nextInt() { int n = 0; skip(); int b = readByte(); while (b >= '0' && b <= '9') { n = n * 10 + (b - '0'); b = readByte(); } return n; } } }

xanadu.java:4: error: class Main is public, should be declared in a file named Main.java
public class Main {
       ^
1 error

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