#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int dirx[4] = { 0, 0, -1, 1 };
const int diry[4] = { 1, -1, 0, 0 };

const int N=1e6+100;
const int mod=1e9+7;
int dp[N][4];

int main() {
    #ifdef LLOCAL
    freopen("a.in", "r", stdin);
    #endif
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int n;
    cin>>n;
    vector<int>a(n+1);
    for(int i=1;i<=n;i++) cin>>a[i];
    ll ans=0;
    for(int i=1;i<=n;i++){
        dp[i][1]=dp[i-1][1]+(a[i]==1);dp[i][1]%=mod;
        dp[i][2]=dp[i-1][2]+(a[i]==2) *(dp[i-1][1]+dp[i-1][2]);
        dp[i][2]%=mod;
        dp[i][3]=dp[i-1][3]+(a[i]==3)*dp[i-1][2]; dp[i][3]%=mod;
        ans+=dp[i][3];
        //ans%=mod;

    }
    cout<<dp[n][3]<<endl;
}