#include <bits/stdc++.h>
using namespace std;
#define INF 1000000000000000000
#define MOD 1000000007
using ll=long long;
using Graph=vector<vector<int>>;

int main(){
  int N;
  cin>>N;
  vector<ll> A(N);
  bool zero=false;
  for(int i=0;i<N;i++){
    cin>>A[i];
    if(A[i]==0){
      zero=true;
    }
  }

  if(zero){
    cout<<-1<<endl;
  }else{
    ll a=1;
    for(int i=0;i<N;i++){
      if(A[i]==1){
        a*=1;
      }else if(A[i]==2){
        a*=4;
      }else if(A[i]==3){
        a*=27*27;
      }else{
        cout<<MOD<<endl;
        break;
      }
      if(a>MOD){
        cout<<MOD<<endl;
        break;
      }
      if(i==N-1){
        cout<<MOD%a<<endl;
      }
    }
  }
}