import java.util.ArrayList;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int a, b;
		ArrayList<Integer> li = new ArrayList<Integer>();
		a = in.nextInt();
		b = in.nextInt();
		int max = Math.max(a, b);
		for (int i = 0; i < max; i++) {
			if (Math.abs((a - i)) == Math.abs((b - i))) {
				li.add(i);
			}
		}
		if (li.size() != 0) {
			for (int i = 0; i < li.size(); i++) {
				if (i != li.size() - 1)
					System.out.print(li.get(i) + " ");
				else
					System.out.println(li.get(i));
			}
		} else
			System.out.println("IMPOSSIBLE");
		in.close();
	}
} import java.util.ArrayList; ArrayList java.util import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int a, b;
		ArrayList<Integer> li = new ArrayList<Integer>();
		a = in.nextInt();
		b = in.nextInt();
		int max = Math.max(a, b);
		for (int i = 0; i < max; i++) {
			if (Math.abs((a - i)) == Math.abs((b - i))) {
				li.add(i);
			}
		}
		if (li.size() != 0) {
			for (int i = 0; i < li.size(); i++) {
				if (i != li.size() - 1)
					System.out.print(li.get(i) + " ");
				else
					System.out.println(li.get(i));
			}
		} else
			System.out.println("IMPOSSIBLE");
		in.close();
	}
} Main public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int a, b;
		ArrayList<Integer> li = new ArrayList<Integer>();
		a = in.nextInt();
		b = in.nextInt();
		int max = Math.max(a, b);
		for (int i = 0; i < max; i++) {
			if (Math.abs((a - i)) == Math.abs((b - i))) {
				li.add(i);
			}
		}
		if (li.size() != 0) {
			for (int i = 0; i < li.size(); i++) {
				if (i != li.size() - 1)
					System.out.print(li.get(i) + " ");
				else
					System.out.println(li.get(i));
			}
		} else
			System.out.println("IMPOSSIBLE");
		in.close();
	} main {
		Scanner in = new Scanner(System.in);
		int a, b;
		ArrayList<Integer> li = new ArrayList<Integer>();
		a = in.nextInt();
		b = in.nextInt();
		int max = Math.max(a, b);
		for (int i = 0; i < max; i++) {
			if (Math.abs((a - i)) == Math.abs((b - i))) {
				li.add(i);
			}
		}
		if (li.size() != 0) {
			for (int i = 0; i < li.size(); i++) {
				if (i != li.size() - 1)
					System.out.print(li.get(i) + " ");
				else
					System.out.println(li.get(i));
			}
		} else
			System.out.println("IMPOSSIBLE");
		in.close();
	} Scanner in = new Scanner(System.in); in new Scanner(System.in) int a a b; b ArrayList<Integer> li = new ArrayList<Integer>(); li new ArrayList<Integer>() a = in.nextInt() a in.nextInt() in.nextInt in b = in.nextInt() b in.nextInt() in.nextInt in int max = Math.max(a, b); max Math.max(a, b) Math.max Math a b for (int i = 0; i < max; i++) {
			if (Math.abs((a - i)) == Math.abs((b - i))) {
				li.add(i);
			}
		} int i = 0; int i = 0; i 0 i < max i max i++ i++ i {
			if (Math.abs((a - i)) == Math.abs((b - i))) {
				li.add(i);
			}
		} {
			if (Math.abs((a - i)) == Math.abs((b - i))) {
				li.add(i);
			}
		} if (Math.abs((a - i)) == Math.abs((b - i))) {
				li.add(i);
			} Math.abs((a - i)) == Math.abs((b - i)) Math.abs((a - i)) Math.abs Math (a - i) a i Math.abs((b - i)) Math.abs Math (b - i) b i {
				li.add(i);
			} li.add(i) li.add li i if (li.size() != 0) {
			for (int i = 0; i < li.size(); i++) {
				if (i != li.size() - 1)
					System.out.print(li.get(i) + " ");
				else
					System.out.println(li.get(i));
			}
		} else
			System.out.println("IMPOSSIBLE"); li.size() != 0 li.size() li.size li 0 {
			for (int i = 0; i < li.size(); i++) {
				if (i != li.size() - 1)
					System.out.print(li.get(i) + " ");
				else
					System.out.println(li.get(i));
			}
		} for (int i = 0; i < li.size(); i++) {
				if (i != li.size() - 1)
					System.out.print(li.get(i) + " ");
				else
					System.out.println(li.get(i));
			} int i = 0; int i = 0; i 0 i < li.size() i li.size() li.size li i++ i++ i {
				if (i != li.size() - 1)
					System.out.print(li.get(i) + " ");
				else
					System.out.println(li.get(i));
			} {
				if (i != li.size() - 1)
					System.out.print(li.get(i) + " ");
				else
					System.out.println(li.get(i));
			} if (i != li.size() - 1)
					System.out.print(li.get(i) + " ");
				else
					System.out.println(li.get(i)); i != li.size() - 1 i li.size() - 1 li.size() li.size li 1 System.out.print(li.get(i) + " ") System.out.print System.out System System.out li.get(i) + " " li.get(i) li.get li i " " System.out.println(li.get(i)) System.out.println System.out System System.out li.get(i) li.get li i System.out.println("IMPOSSIBLE") System.out.println System.out System System.out "IMPOSSIBLE" in.close() in.close in String[] args args public class Main {
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int a, b;
		ArrayList<Integer> li = new ArrayList<Integer>();
		a = in.nextInt();
		b = in.nextInt();
		int max = Math.max(a, b);
		for (int i = 0; i < max; i++) {
			if (Math.abs((a - i)) == Math.abs((b - i))) {
				li.add(i);
			}
		}
		if (li.size() != 0) {
			for (int i = 0; i < li.size(); i++) {
				if (i != li.size() - 1)
					System.out.print(li.get(i) + " ");
				else
					System.out.println(li.get(i));
			}
		} else
			System.out.println("IMPOSSIBLE");
		in.close();
	}
} public class Main {
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int a, b;
		ArrayList<Integer> li = new ArrayList<Integer>();
		a = in.nextInt();
		b = in.nextInt();
		int max = Math.max(a, b);
		for (int i = 0; i < max; i++) {
			if (Math.abs((a - i)) == Math.abs((b - i))) {
				li.add(i);
			}
		}
		if (li.size() != 0) {
			for (int i = 0; i < li.size(); i++) {
				if (i != li.size() - 1)
					System.out.print(li.get(i) + " ");
				else
					System.out.println(li.get(i));
			}
		} else
			System.out.println("IMPOSSIBLE");
		in.close();
	}
} Main
import java.util.ArrayList;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int a, b;
		ArrayList<Integer> li = new ArrayList<Integer>();
		a = in.nextInt();
		b = in.nextInt();
		int max = Math.max(a, b);
		for (int i = 0; i < max; i++) {
			if (Math.abs((a - i)) == Math.abs((b - i))) {
				li.add(i);
			}
		}
		if (li.size() != 0) {
			for (int i = 0; i < li.size(); i++) {
				if (i != li.size() - 1)
					System.out.print(li.get(i) + " ");
				else
					System.out.println(li.get(i));
			}
		} else
			System.out.println("IMPOSSIBLE");
		in.close();
	}
}
