#include using namespace std; using ll = long long; template using vec = vector; template using vvec = vector>; constexpr ll mod = 1e9+7; struct mint { ll x; mint(ll x=0):x((x%mod+mod)%mod){} friend ostream &operator<<(ostream& os,const mint& a){ return os << a.x; } friend istream &operator>>(istream& is,mint& a){ ll t; is >> t; a = mint(t); return (is); } mint& operator+=(const mint a) { if ((x += a.x) >= mod) x -= mod; return *this; } mint& operator-=(const mint a) { if ((x += mod-a.x) >= mod) x -= mod; return *this; } mint& operator*=(const mint a) { (x *= a.x) %= mod; return *this; } mint operator+(const mint a) const { mint res(*this); return res+=a; } mint operator-(const mint a) const { mint res(*this); return res-=a; } mint operator*(const mint a) const { mint res(*this); return res*=a; } mint pow(ll t) const { if (!t) return 1; mint a = pow(t>>1); a *= a; if (t&1) a *= *this; return a; } // for prime mod mint inv() const { return pow(mod-2); } mint& operator/=(const mint a) { return (*this) *= a.inv(); } mint operator/(const mint a) const { mint res(*this); return res/=a; } }; int main(){ cin.tie(0); ios::sync_with_stdio(false); int N; cin >> N; vec A(N); bool zero = false; for(auto& x:A){ cin >> x; zero |= !x; } if(zero){ cout << 0 << "\n"; return 0; } A.push_back(1); mint ans = 1; vec ne(N+1,-1); ne[N-1] = N; for(int i=N-2;i>=0;i--){ if(A[i+1]==1) ne[i] = ne[i+1]; else if(A[i+1]>=2) ne[i] = i+1; } // for(int i=0;i=inf) break; now = ne[now]; } // cerr << val << " " << ans << "\n"; } cout << ans << "\n"; }