[백준] 29736번 브실이와 친구가 되고 싶어(bronze 4

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


public class Main{
    public static void main(String[] args) throws IOException{
        BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
        BufferedWriter bw=new BufferedWriter(new OutputStreamWriter(System.out));
        StringTokenizer st=new StringTokenizer(br.readLine());
        int a=Integer.parseInt(st.nextToken());
        int b=Integer.parseInt(st.nextToken());

        st=new StringTokenizer(br.readLine());
        int k=Integer.parseInt(st.nextToken());
        int x=Integer.parseInt(st.nextToken());
        int answer=0;
        for(int i=a; i<=b; i++){
            answer = Math.abs(k-i)<=x ? answer+1 :answer;
        }
        bw.write(answer==0 ? "IMPOSSIBLE" :answer+"");
        bw.flush();
    }
}