import java.io.InputStream;
import java.io.PrintWriter;
import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.PriorityQueue;
import java.util.Scanner;
import java.util.Set;
import java.util.Stack;
import java.util.TreeMap;
import java.util.TreeSet;

import static java.util.Comparator.*;

public class Main {
    public static void main(String[] args) {
        PrintWriter out = new PrintWriter(System.out);
        Solver solver = new Solver(System.in, out);
        solver.solve();
        out.close();
    }
}
class Solver {
	Scanner sc;
	PrintWriter out;
    public Solver(InputStream in, PrintWriter out) {
    	sc = new Scanner(in);
    	this.out = out;
    }
    // ==================================================================
    // 単純な素因数分解							
    Map<Long, Long> dec(long n){							
    	// 割った数を保存するマップ　３で２回割れたら、ans.get(3) == 2　となる						
    	Map<Long, Long> ans = new HashMap<Long, Long>();						
            							
    	long num = n;						
    	Long wk = 0L;						
    	// ２　～　ルートｎ　の間、繰り返す						
    	for(long i = 2; i * i <= n && num != 1; ++i){						
    		// i で割り切れる間、割る					
    		while(num % i == 0){					
    			num /= i;				
    			wk = ans.get(i);				
    			if(wk == null) {				
    				ans.put(i, 1L);			
    			} else {				
    				ans.replace(i, (wk+1L));			
    			}				
    		}					
    	}						
    	if(num != 1) {						
    		wk = ans.get(num);// 最後に残った数も含める					
    		if(wk == null) {					
    			ans.put(num, 1L);				
    		} else {					
    			ans.replace(num, (wk+1L));				
    		}					
    	}						
    	return ans;						
    }							
    Map<Long, Map<Long, Long>> DEC = new HashMap<>();
    public void solve() {
    	long N = Integer.parseInt(sc.next());
    	int K = Integer.parseInt(sc.next());
    	for (long i = 1; i <= N; i++) {
			DEC.put(i, dec(i));
		}
    	long cnt, max = -1, ans = -1, wk;
    	for (long i = 1; i < N; i++) {
			if(DEC.get(i) == null)	continue;
    		cnt = 0;
    		for (long key : DEC.get(N).keySet()) {
    			if(DEC.get(i).get(key) == null)	continue;
//    			out.println(" i = " + i + "  key = " + key + "  min("
//    					 + DEC.get(i).get(key) + ", " + DEC.get(N).get(key) + ")");
				cnt += Math.min(DEC.get(i).get(key), DEC.get(N).get(key));
			}
//    		out.println("[" + i + "]  の共通の素因数の数  = " + cnt);
    		if(cnt < K)		continue;
    		wk = 1;
    		for (long key : DEC.get(i).keySet()) {
				wk *= (DEC.get(i).get(key) + 1);
			}
//    		out.println("[" + i + "]  の約数の数  = " + wk);
    		if(max < wk) {	max = wk;	ans = i;	}
    	}
    	out.println(ans);
    }
    // ==================================================================
}