//#define _GLIBCXX_DEBUG #include #define rep(i, n) for(int i=0; i; using vs = vector; using vi = vector; using vvi = vector; template using PQ = priority_queue; template using PQG = priority_queue, greater >; const int INF = 0xccccccc; const ll LINF = 0xcccccccccccccccLL; template inline bool chmax(T1 &a, T2 b) {return a < b && (a = b, true);} template inline bool chmin(T1 &a, T2 b) {return a > b && (a = b, true);} template istream &operator>>(istream &is, pair &p) { return is >> p.first >> p.second;} template ostream &operator<<(ostream &os, const pair &p) { return os << p.first << ' ' << p.second;} //const unsigned int mod = 1000000007; const unsigned int mod = 998244353; struct mint { unsigned int x; mint():x(0) {} mint(int64_t x_) { int64_t v = int64_t(x_ % mod); if(v < 0) v += mod; x = (unsigned int)v; } static mint row(int v) { mint v_; v_.x = v; return v_; } mint operator-() const { return mint(-x);} 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) { uint64_t z = x; z *= a.x; x = (unsigned int)(z % mod); return *this; } mint operator+(const mint a) const { return mint(*this) += a;} mint operator-(const mint a) const { return mint(*this) -= a;} mint operator*(const mint a) const { return mint(*this) *= a;} friend bool operator==(const mint &a, const mint &b) {return a.x == b.x;} friend bool operator!=(const mint &a, const mint &b) {return a.x != b.x;} mint &operator++() { x++; if(x == mod) x = 0; return *this; } mint &operator--() { if(x == 0) x = mod; x--; return *this; } mint operator++(int) { mint result = *this; ++*this; return result; } mint operator--(int) { mint result = *this; --*this; return result; } mint pow(int64_t t) const { mint x_ = *this, r = 1; while(t) { if(t&1) r *= x_; x_ *= x_; t >>= 1; } return r; } //for prime mod mint inv() const { return pow(mod-2);} mint& operator/=(const mint a) { return *this *= a.inv();} mint operator/(const mint a) {return mint(*this) /= a;} }; istream& operator>>(istream& is, mint& a) { return is >> a.x;} ostream& operator<<(ostream& os, const mint& a) { return os << a.x;} #define N 200100 //head int n; int a[N]; mint sum[N], _sum[N]; vi pl; bitset pm; mint ans; int main() { ios::sync_with_stdio(false); cin.tie(0); cin >> n; rep(i, n) { int u; cin >> u; if(abs(u) != 1) pl.push_back(i); a[i] = u; if(pm.test(i)) pm.set(i+1); if(u < 0) pm.flip(i+1); sum[i+1] = sum[i]; if(pm.test(i+1)) sum[i+1] += (i == n-1?mint(1):mint(2).pow(n-2-i)); _sum[i+1] = _sum[i] + (i == n-1?mint(1):mint(2).pow(n-2-i)); } pl.push_back(n); //rep(i, n+1) cerr << sum[i] << endl; rep(i, n) { auto itr = lower_bound(all(pl), i); if(*itr == n or a[*itr] == 0) { continue; } auto utr = next(itr); mint s = sum[*utr] - sum[*itr]; mint z = _sum[*utr] - _sum[*itr];; if((pm.test(i) != pm.test(*itr+1)) != pm.test(*itr+1)) s = z-s; ans += s * mint(2).pow(i?i-1:0); } cout << ans*mint((mod+1)>>1).pow(n-1) << endl; }