import java.util.*;
import java.io.*;
import java.lang.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        long a = sc.nextInt();
        long b = sc.nextInt();

        long c = (b*b)-(a*a);
        long d = 2*b-2*a;

        if (c%d == 0)
            System.out.println(c/d);
        else
            System.out.println("IMPOSSIBLE");
    }
} import java.util.*; util.* java import java.io.*; io.* java import java.lang.*; lang.* java public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        long a = sc.nextInt();
        long b = sc.nextInt();

        long c = (b*b)-(a*a);
        long d = 2*b-2*a;

        if (c%d == 0)
            System.out.println(c/d);
        else
            System.out.println("IMPOSSIBLE");
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        long a = sc.nextInt();
        long b = sc.nextInt();

        long c = (b*b)-(a*a);
        long d = 2*b-2*a;

        if (c%d == 0)
            System.out.println(c/d);
        else
            System.out.println("IMPOSSIBLE");
    } main {
        Scanner sc = new Scanner(System.in);

        long a = sc.nextInt();
        long b = sc.nextInt();

        long c = (b*b)-(a*a);
        long d = 2*b-2*a;

        if (c%d == 0)
            System.out.println(c/d);
        else
            System.out.println("IMPOSSIBLE");
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) long a = sc.nextInt(); a sc.nextInt() sc.nextInt sc long b = sc.nextInt(); b sc.nextInt() sc.nextInt sc long c = (b*b)-(a*a); c (b*b)-(a*a) (b*b) b b (a*a) a a long d = 2*b-2*a; d 2*b-2*a 2*b 2 b 2*a 2 a if (c%d == 0)
            System.out.println(c/d);
        else
            System.out.println("IMPOSSIBLE"); c%d == 0 c%d c d 0 System.out.println(c/d) System.out.println System.out System System.out c/d c d System.out.println("IMPOSSIBLE") System.out.println System.out System System.out "IMPOSSIBLE" String[] args args public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        long a = sc.nextInt();
        long b = sc.nextInt();

        long c = (b*b)-(a*a);
        long d = 2*b-2*a;

        if (c%d == 0)
            System.out.println(c/d);
        else
            System.out.println("IMPOSSIBLE");
    }
} public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        long a = sc.nextInt();
        long b = sc.nextInt();

        long c = (b*b)-(a*a);
        long d = 2*b-2*a;

        if (c%d == 0)
            System.out.println(c/d);
        else
            System.out.println("IMPOSSIBLE");
    }
} Main
import java.util.*;
import java.io.*;
import java.lang.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        long a = sc.nextInt();
        long b = sc.nextInt();

        long c = (b*b)-(a*a);
        long d = 2*b-2*a;

        if (c%d == 0)
            System.out.println(c/d);
        else
            System.out.println("IMPOSSIBLE");
    }
}
