Codeforces Round #203 (Div. 2) A TL

// Codeforces Round #203 (Div. 2) A TL
// Problem: http://codeforces.com/contest/350/problem/A

import java.io.*;
import java.math.*;
import java.util.*;

//Codeforces
public class MainCodeforces1 {
private static MyScanner in;
private static PrintStream out;
private static boolean LOCAL_TEST = false;

private static void solve() throws IOException
{
int n = in.nextInt();
int m = in.nextInt();
int[] a = new int[n];
int[] b = new int[m];
for (int i = 0; i < a.length; i++) {
a[i] = in.nextInt();
}
for (int i = 0; i < b.length; i++) {
b[i] = in.nextInt();
}
for (int v = 1; v <= 100; v++) {
int nExtra = 0;
boolean allCorrectPass = true;
for (int j = 0; j < a.length; j++) {
if (a[j] > v) {
allCorrectPass = false;
break;
}
if (2 * a[j] <= v)
nExtra++;
}
boolean allWrongFailed = true;
for (int i = 0; i < b.length; i++) {
if (b[i] <= v) {
allWrongFailed = false;
break;
}
}
if (allCorrectPass && nExtra > 0 && allWrongFailed) {
out.println(v);
return;
}
}
out.println(-1);
}

public static void main(String[] args) throws IOException {
// helpers for input/output
out = System.out;
try {
String cname = System.getenv("COMPUTERNAME");
if (!cname.equals(""))
LOCAL_TEST = true;
} catch (Exception e) {
}
if (LOCAL_TEST) {
in = new MyScanner("E:\\zin.txt");
}
else {
boolean usingFileForIO = false;
if (usingFileForIO) {
// using input.txt and output.txt as I/O
in = new MyScanner("input.txt");
out = new PrintStream("output.txt");
}
else {
in = new MyScanner();
out = System.out;
}
}

solve();
}

// =====================================
static class MyScanner {
BufferedReader bufReader;
StringTokenizer strTok;

public MyScanner() throws IOException
{
bufReader = new BufferedReader(new InputStreamReader(System.in));
strTok = new StringTokenizer("");
}

public MyScanner(String inputFile) throws IOException {
bufReader = new BufferedReader(new InputStreamReader(new FileInputStream(
inputFile)));
strTok = new StringTokenizer("");
}

String GetNextToken() throws IOException {
if (!strTok.hasMoreTokens())
strTok = new StringTokenizer(bufReader.readLine());
return strTok.nextToken();
}

public int nextInt() throws IOException {
return Integer.valueOf(GetNextToken());
}

public long nextLong() throws IOException {
return Long.valueOf(GetNextToken());
}

public double nextDouble() throws IOException {
return Double.valueOf(GetNextToken());
}

public String nextString() throws IOException {
return GetNextToken();
}

public String nextLine() throws IOException {
return bufReader.readLine();
}

public int countTokens() {
return strTok.countTokens();
}

public boolean hasMoreTokens() {
return strTok.hasMoreTokens();
}
}

}