import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner scan=new Scanner(System.in);
        int n=scan.nextInt();
        int[] prime=new int[20005];
        int i;
        int j;
        int x=0;
        for ( i = 3; i <20005; i+=2) {
            for ( j = 2; j <i ; j++) {
                if(i%j==0){
                    break;
                }
            }
            if (i==j) {
                prime[x++]=i;
            }
        }
        int max=0;
        for (int k = 0; k < prime.length; k++) {
            for (int k2 = k+1; k2 < prime.length; k2++) {
                if(prime[k]+prime[k2]==n){
                    if(max<prime[k]*prime[k2]){
                        max=prime[k]*prime[k2];
                        continue;
                    }
                }
            }
        }
        System.out.print(max);
        scan.close();
    }
}


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基本思路就是把用数组把质数求出来然后 挨个测试，样例过了，呜呜呜不知道为啥50分