#include <bits/stdc++.h>

using namespace std;

int N, K, p_num;
bool arr[200000];
int prime[18000] = {0};
bool used[10];
int dp[18000] = {0};
//dp[素数列の長さ] = 素数

void Eratosthenes(){
    for(int i = 0; i <= N; i++) arr[i] = true;
	for(int i = 2; i <= sqrt(N); i++){
		if(arr[i]){
			for(int j = 0; i * (j + 2) < N; j++){
				arr[i *(j + 2)] = false;
			}
		}
	}
	int j = 0;
	for(int i = K; i <= N; i++){
		if(arr[i]){
			if(i != 1) prime[j++] = i;
		}
	}
	p_num = j;
}

int Hash(int num){
    string sum = to_string(num);
    while(sum.size() != 1){
        num = 0;
        while(!sum.empty()){
            num += sum[sum.size()- 1] - '0';
            sum.pop_back();
        }
        sum = to_string(num);
    }
    return sum[0] - '0';
}

int main(void){
    
    cin >> K >> N;
    
    Eratosthenes();
    
    for(int i = 0; i < p_num; ++i){
        int j, h_num;
        for(j = 0; j < 10; ++j) used[j] = false;
        for(j = 0; j < p_num && !used[(h_num = Hash(prime[i + j]))]; ++j) used[h_num] = true;
        if(dp[j] < prime[i]) dp[j] = prime[i]; 
    }
    
    for(int i = p_num; i >= 0; --i){
        if(dp[i] != 0){
            cout << dp[i] << endl;
            break;
        }
    }
    
    return 0;
}