#include <iostream>
using namespace std;
int main(){
    int n;cin>>n;
    long long r = 1;
    long long A[3] = {1,4,729};
    int ret = 0;
    for(int i = 0; n > i; i++){
        int x;cin>>x;
        if(x >= 4){
            if(ret != -2)ret = -1;
        }else if(x == 0){
            ret = -2;
        }
        if(ret != 0)continue;
        r *= A[x-1];
        if(r > 1000000007){
            if(ret != -2)ret = -1;
        }
    }
    if(ret == 0)cout << 1000000007%r << endl;
    else if(ret == -1)cout << 1000000007 << endl;
    else cout << -1 << endl;
}