#include using namespace std; #define ALL(x) x.begin(),x.end() #define rep(i,n) for(int i=0;i<(n);i++) #define debug(v) cout<<#v<<":";for(auto x:v){cout<bool chmax(T &a,const T &b){if(abool chmin(T &a,const T &b){if(b ostream &operator<<(ostream &os,const pair&p){ os< ostream &operator<<(ostream &os,const vector&v){ for(int i=0;i<(int)v.size();i++) os< istream &operator>>(istream &is,pair&p){ is>>p.first>>p.second; return is; } template istream &operator>>(istream &is,vector&v){ for(T &x:v)is>>x; return is; } template struct ModInt{ long long x; ModInt():x(0){} ModInt(long long y):x(y>=0?y%Mod:(Mod-(-y)%Mod)%Mod){} ModInt &operator+=(const ModInt &p){ if((x+=p.x)>=Mod) x-=Mod; return *this; } ModInt &operator-=(const ModInt &p){ if((x+=Mod-p.x)>=Mod)x-=Mod; return *this; } ModInt &operator*=(const ModInt &p){ x=(int)(1ll*x*p.x%Mod); return *this; } ModInt &operator/=(const ModInt &p){ (*this)*=p.inverse(); return *this; } ModInt operator-()const{return ModInt(-x);} ModInt operator+(const ModInt &p)const{return ModInt(*this)+=p;} ModInt operator-(const ModInt &p)const{return ModInt(*this)-=p;} ModInt operator*(const ModInt &p)const{return ModInt(*this)*=p;} ModInt operator/(const ModInt &p)const{return ModInt(*this)/=p;} ModInt operator==(const ModInt &p)const{return x==p.x;} ModInt operator!=(const ModInt &p)const{return x!=p.x;} ModInt inverse()const{ int a=x,b=Mod,u=1,v=0,t; while(b>0){ t=a/b; swap(a-=t*b,b);swap(u-=t*v,v); } return ModInt(u); } ModInt pow(long long n)const{ ModInt ret(1),mul(x); while(n>0){ if(n&1) ret*=mul; mul*=mul;n>>=1; } return ret; } friend ostream &operator<<(ostream &os,const ModInt &p){return os<>(istream &is,ModInt &a){long long t;is>>t;a=ModInt(t);return (is);} static int get_mod(){return Mod;} }; using mint=ModInt; template struct comcalc{ vector fact,finv,inv; comcalc():fact(MAX),finv(MAX),inv(MAX){ fact[0]=mint(1),fact[1]=mint(1),finv[0]=mint(1),finv[1]=mint(1),inv[1]=mint(1); for(int i=2;ir)return mint(0); mint ret=mint(r+1)*com(n+r+1,r+1)-mint(l)*com(l+n,l); ret/=mint(n+1); return ret; } }; const int MAX=4010000; using cominit=comcalc; const ll mod2=924844033; using mint2=ModInt; using P=pair; int n; // zero-sum ranges mint solve(vector v){ mint ret=0; map mp; mint x=1; mint2 x2=1; mint y=mint(-2).inverse(); mint2 y2=mint2(-2).inverse(); mp[{1,1}]+=1; rep(i,(int)v.size()){ x*=mint(v[i]);x2*=mint2(v[i]); mint need=x*y;mint2 need2=x2*y2; mint i2=mint(2).pow(i+1); ret+=mp[{need.x,need2.x}]/i2; mp[{x.x,x2.x}]+=i2; } return ret; } signed main(){ cin>>n; assert(n<=1000); vector a(n); cin>>a; mint res=0; for(int i=1;i v; for(int j=i-1;j>0;j--){ if(abs(a[j])!=1) break; v.push_back(a[j]); } reverse(ALL(v)); v.push_back(a[i]); for(int j=i+1;j2) break; } } if(f){ reverse(ALL(a)); int x=1; rep(i,n){ x*=a[i]; if(x==-2){ if(i==n-1) res+=1,f=false; else{ res+=mint(2).pow(n-2-i); } } if(abs(x)==0 or abs(x)>2) break; } } cout<