#include using namespace std; #define rep(i, n) for(int i = 0; i < n; i++) #define rep2(i, x, n) for(int i = x; i <= n; i++) #define rep3(i, x, n) for(int i = x; i >= n; i--) #define elif else if #define sp(x) fixed << setprecision(x) #define pb push_back #define eb emplace_back #define all(x) x.begin(), x.end() #define sz(x) (int)x.size() using ll = long long; using pii = pair; using pil = pair; using pli = pair; using pll = pair; //const int MOD = 1000000007; const int MOD = 998244353; const int inf = (1<<30)-1; const ll INF = (1LL<<60)-1; const double pi = acos(-1.0); const double EPS = 1e-10; template bool chmax(T &x, const T &y) {return (x < y)? (x = y, true) : false;}; template bool chmin(T &x, const T &y) {return (x > y)? (x = y, true) : false;}; template struct Mod_Int{ ll x; Mod_Int() : x(0) {} Mod_Int(ll y) : x(y >= 0 ? y % mod : (mod - (-y) % mod) % mod) {} Mod_Int &operator += (const Mod_Int &p){ x = (x + p.x) % mod; return *this; } Mod_Int &operator -= (const Mod_Int &p){ x = (x + mod - p.x) % mod; return *this; } Mod_Int &operator *= (const Mod_Int &p){ x = (x * p.x) % mod; return *this; } Mod_Int &operator /= (const Mod_Int &p){ *this *= p.inverse(); return *this; } Mod_Int &operator ++ () {return *this += Mod_Int(1);} Mod_Int operator ++ (int){ Mod_Int tmp = *this; ++*this; return tmp; } Mod_Int &operator -- () {return *this -= Mod_Int(1);} Mod_Int operator -- (int){ Mod_Int tmp = *this; --*this; return tmp; } Mod_Int operator - () const {return Mod_Int(-x);} Mod_Int operator + (const Mod_Int &p) const {return Mod_Int(*this) += p;} Mod_Int operator - (const Mod_Int &p) const {return Mod_Int(*this) -= p;} Mod_Int operator * (const Mod_Int &p) const {return Mod_Int(*this) *= p;} Mod_Int operator / (const Mod_Int &p) const {return Mod_Int(*this) /= p;} bool operator == (const Mod_Int &p) const {return x == p.x;} bool operator != (const Mod_Int &p) const {return x != p.x;} Mod_Int inverse() const { assert(*this != Mod_Int(0)); return pow(mod-2); } Mod_Int pow(ll k) const{ Mod_Int now = *this, ret = 1; while(k){ if(k&1) ret *= now; now *= now, k >>= 1; } return ret; } friend ostream &operator << (ostream &os, const Mod_Int &p){ return os << p.x; } friend istream &operator >> (istream &is, Mod_Int &p){ ll a; is >> a; p = Mod_Int(a); return is; } }; using mint = Mod_Int; int main(){ int N; cin >> N; int a[N]; rep(i, N) cin >> a[i]; mint ans = 0; mint pw[N+1]; pw[0] = 1; rep(i, N) pw[i+1] = pw[i]*2; rep(i, N){ if(abs(a[i]) != 2) continue; mint l1 = 0, l2 = 0, r1 = 0, r2 = 0; int s = 1, ptr = i; while(ptr < N){ if(s == 1) r1 += pw[max(0, N-2-ptr)]; elif(s == -1) r2 += pw[max(0, N-2-ptr)]; else break; if(ptr == N-1) break; s *= a[++ptr]; } s = 1, ptr = i; while(ptr >= 0){ if(s == 1) l1 += pw[max(0, ptr-1)]; elif(s == -1) l2 += pw[max(0, ptr-1)]; else break; if(ptr == 0) break; s *= a[--ptr]; } if(a[i] == -2) ans += l1*r1+l2*r2; else ans += l1*r2+l2*r1; } cout << ans/pw[N-1] << endl; }