B题java代码请求大家帮忙看一下哪里出问题了

import java.math.*;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.io.StreamTokenizer;
import java.util.*;
public class Main {
    public static void main(String args[])throws IOException
    {
        StreamTokenizer in = new StreamTokenizer(new BufferedReader(new InputStreamReader(System.in)));
        PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));
            in.nextToken();
            int n = (int)in.nval;
            in.nextToken();
            int k = (int)in.nval;
            in.nextToken();
            String x = in.sval;
            String sum="";
            String sums="";
            for(int t=0;t<n/k;t++)
            {
                if(t>0)
                x = x.substring(1)+x.charAt(0);
                sum=x.substring(0,k);
                for(int i=k;i<n;i+=k)
            {
                if((x.substring(i,i+k)).compareTo(sum)>0)
                {
                    sum = x.substring(i,i+k);
                    continue;
                }
            }
                if(t==0)
                    sums = sum;
                else{
                     if(sums.compareTo(sum)>0)
                    sums = sum;
                }
                
            }
            out.print(sums);
        out.flush();
    }
                  }