#include <bits/stdc++.h>
using namespace std;

const int maxn = 1e4 + 1;

int prime[maxn];

int ans[maxn];

void getPrime(){
    memset(prime, 0, sizeof(prime));
    for(int i = 2; i <= maxn; i++){
        if(0 == prime[i]){
            prime[++prime[0]] = i;
        }
        for(int j = 1; j <= prime[0] && i * prime[j] <= maxn; j++){
            prime[i * prime[j]] = 1;
            if(0 == i % prime[j]){
                break;
            }
        }
    }
    return;
}

int main(){
    getPrime();
    int n;
    while(cin>>n){
        int pos = 0;
        for(int i = 1; i <= prime[0] && prime[i] < n; i++){
            if(1 == prime[i] % 10){
                ans[pos++] = prime[i];
            }
        }
        if(0 == pos){
            cout<<-1<<endl;
            continue;
        }
        else{
            cout<<ans[0];
            for(int i = 1; i < pos; i++){
         ...