Language: Java

import java.io.BufferedOutputStream;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.util.Scanner;
import java.lang.*;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import static java.util.Collections.list;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Random;
import java.util.Set;
import java.util.StringTokenizer;
import java.util.TreeSet;
public class Lab4 {
    
    
    static class FastReader 
    { 
        BufferedReader br; 
        StringTokenizer st; 
  
        public FastReader() 
        { 
            br = new BufferedReader(new
                     InputStreamReader(System.in)); 
        } 
  
        String next() 
        { 
            while (st == null || !st.hasMoreElements()) 
            { 
                try
                { 
                    st = new StringTokenizer(br.readLine()); 
                } 
                catch (IOException  e) 
                { 
                    e.printStackTrace(); 
                } 
            } 
            return st.nextToken(); 
        } 
  
        int nextInt() 
        { 
            return Integer.parseInt(next()); 
        } 
  
        long nextLong() 
        { 
            return Long.parseLong(next()); 
        } 
  
        double nextDouble() 
        { 
            return Double.parseDouble(next()); 
        } 
  
        String nextLine() 
        { 
            String str = ""; 
            try
            { 
                str = br.readLine(); 
            } 
            catch (IOException e) 
            { 
                e.printStackTrace(); 
            } 
            return str; 
        } 
    } 
    
    static class BufPrint
    {
        final BufferedWriter bw;
        public BufPrint()
        {
            this.bw=new BufferedWriter(new OutputStreamWriter(System.out));
        }
        public void print(Object object)throws IOException
        {
            bw.append(""+object);
        }
        public void println(Object object)throws IOException
        {
            print(object);
            bw.append("\n");
        }
        public void close()throws IOException
        {
            bw.close();
        }
    }
    

        public static int GCD(int l,int r) {
        int gcd=1;
        for(int i = 1; i <= l && i <= r; ++i)
        {
            if(l % i==0 && r % i==0)
                gcd = i;
        }
    return gcd;
}
    
    public static void main(String[] args) throws IOException{
        
            FastReader sc=new FastReader(); 
            BufPrint bp=new BufPrint();
          
                int k=sc.nextInt();
                int a=sc.nextInt();
                int b=sc.nextInt();
                boolean flag=false;
                for(int i=a;i<=b;i++){
                    if(i%k==0)
                    {
                        flag=true;
                        break;
                    }
               }
                if(flag==true)
                {
                    bp.println("OK");
                }
                else
                    bp.println("NG");



                bp.close();
            
    }
    
}

Compiler output:
Main.java:24: error: class Lab4 is public, should be declared in a file named Lab4.java
public class Lab4 {
       ^
1 error