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

bool IsPrime(long num){
    if (num < 2) return false;
    else if (num == 2) return true;
    else if (num % 2 == 0) return false;

    double sqrtNum = sqrt(num);
    for (int i = 3; i <= sqrtNum; i += 2){
        if (num % i == 0){
            return false;}}
    return true;}

int main(){
    long n,i,p=1,ans,j,k,l;
    cin>>n;
    int a[n];
    int t[3*n];
    t[1]=1;
    for(i=2;i-3*n;++i)t[i]=t[i-1]*10;
    for(i=0;i-n;++i)cin>>a[i],p*=2;
    long s[512]={},m=0;
    for(i=0;i-p;++i){
         k=i;
         ans=a[0];
         l=a[0]>9?2:1;
         for(j=1;j-n;++j){
             l+=a[j]>9?2:1;
             if(k%2)ans+=a[j]*t[l];
             else{ans*=a[j]>9?100:10;ans+=a[j];}
             k/=2;}
         if(IsPrime(ans))s[m++]=ans;}
    int max=0;
    for(i=0;i-512;++i)max=max>s[i]?max:s[i];
    cout<<max<<"\n";
}