#line 1 "library/Template/template.hpp" #include using namespace std; #define rep(i,a,b) for(int i=(int)(a);i<(int)(b);i++) #define ALL(v) (v).begin(),(v).end() using ll=long long int; const int inf = 0x3fffffff; const ll INF = 0x1fffffffffffffff; templateinline bool chmax(T& a,T b){if(ainline bool chmin(T& a,T b){if(a>b){a=b;return 1;}return 0;} #line 2 "library/Utility/fastio.hpp" #include class FastIO{ static constexpr int L=1<<16; char rdbuf[L]; int rdLeft=0,rdRight=0; inline void reload(){ int len=rdRight-rdLeft; memmove(rdbuf,rdbuf+rdLeft,len); rdLeft=0,rdRight=len; rdRight+=fread(rdbuf+len,1,L-len,stdin); } inline bool skip(){ for(;;){ while(rdLeft!=rdRight and rdbuf[rdLeft]<=' ')rdLeft++; if(rdLeft==rdRight){ reload(); if(rdLeft==rdRight)return false; } else break; } return true; } template::value,int> =0>inline bool _read(T& x){ if(!skip())return false; if(rdLeft+20>=rdRight)reload(); bool neg=false; if(rdbuf[rdLeft]=='-'){ neg=true; rdLeft++; } x=0; while(rdbuf[rdLeft]>='0' and rdLeft::value,int> =0>inline bool _read(T& x){ if(!skip())return false; if(rdLeft+20>=rdRight)reload(); bool neg=false; if(rdbuf[rdLeft]=='-'){ neg=true; rdLeft++; } x=0; while(rdbuf[rdLeft]>='0' and rdbuf[rdLeft]<='9' and rdLeft='0' and rdbuf[rdLeft]<='9' and rdLeft=rdRight)reload(); x=rdbuf[rdLeft++]; return true; } inline bool _read(string& x){ if(!skip())return false; for(;;){ int pos=rdLeft; while(pos' ')pos++; x.append(rdbuf+rdLeft,pos-rdLeft); if(rdLeft==pos)break; rdLeft=pos; if(rdLeft==rdRight)reload(); else break; } return true; } templateinline bool _read(vector& v){ for(auto& x:v){ if(!_read(x))return false; } return true; } char wtbuf[L],tmp[50]; int wtRight=0; inline void flush(){ fwrite(wtbuf,1,wtRight,stdout); wtRight=0; } inline void _write(const char& x){ if(wtRight>L-32)flush(); wtbuf[wtRight++]=x; } inline void _write(const string& x){ for(auto& c:x)_write(c); } template::value,int> =0>inline void _write(T x){ if(wtRight>L-32)flush(); if(x==0){ _write('0'); return; } else if(x<0){ _write('-'); if (__builtin_expect(x == std::numeric_limits::min(), 0)) { switch (sizeof(x)) { case 2: _write("32768"); return; case 4: _write("2147483648"); return; case 8: _write("9223372036854775808"); return; } } x=-x; } int pos=0; while(x!=0){ tmp[pos++]=char((x%10)|48); x/=10; } rep(i,0,pos)wtbuf[wtRight+i]=tmp[pos-1-i]; wtRight+=pos; } templateinline void _write(const vector& v){ rep(i,0,v.size()){ if(i)_write(' '); _write(v[i]); } } public: FastIO(){} ~FastIO(){flush();} inline void read(){} template inline void read(Head& head,Tail&... tail){ assert(_read(head)); read(tail...); } templateinline void write(){if(ln)_write('\n');} template inline void write(const Head& head,const Tail&... tail){ if(space)_write(' '); _write(head); write(tail...); } }; /** * @brief Fast IO */ #line 3 "sol.cpp" #line 2 "library/Math/modint.hpp" templatestruct fp { int v; static int get_mod(){return mod;} int inv() const{ int tmp,a=v,b=mod,x=1,y=0; while(b)tmp=a/b,a-=tmp*b,swap(a,b),x-=tmp*y,swap(x,y); if(x<0){x+=mod;} return x; } fp(ll x=0){init(x%mod+mod);} fp& init(ll x){v=(x=0); fp res=1,b=*this; while(t){if(t&1)res*=b;b*=b;t>>=1;} return res;} fp& operator+=(const fp& x){return init(v+x.v);} fp& operator-=(const fp& x){return init(v+mod-x.v);} fp& operator*=(const fp& x){v=ll(v)*x.v%mod; return *this;} fp& operator/=(const fp& x){v=ll(v)*x.inv()%mod; return *this;} fp operator+(const fp& x)const{return fp(*this)+=x;} fp operator-(const fp& x)const{return fp(*this)-=x;} fp operator*(const fp& x)const{return fp(*this)*=x;} fp operator/(const fp& x)const{return fp(*this)/=x;} bool operator==(const fp& x)const{return v==x.v;} bool operator!=(const fp& x)const{return v!=x.v;} friend istream& operator>>(istream& is,fp& x){return is>>x.v;} friend ostream& operator<<(ostream& os,const fp& x){return os<struct factorial { vector Fact,Finv,Inv; factorial(int maxx){ Fact.resize(maxx); Finv.resize(maxx); Inv.resize(maxx); Fact[0]=Fact[1]=Finv[0]=Finv[1]=Inv[1]=1; rep(i,2,maxx){Fact[i]=Fact[i-1]*i;} Finv[maxx-1]=Fact[maxx-1].inv(); for(int i=maxx-1;i>=2;i--){Finv[i-1]=Finv[i]*i; Inv[i]=Finv[i]*Fact[i-1];} } T fact(int n,bool inv=0){if(n<0)return 0; return (inv?Finv[n]:Fact[n]);} T inv(int n){if(n<0)return 0; return Inv[n];} T nPr(int n,int r,bool inv=0){if(n<0||n; factorial fact(2010101); FastIO io; int main(){ int n; io.read(n); vector a(n); io.read(a); auto encode=[&](vector& p)->vector{ vector ret; rep(_,0,p[0])ret.push_back(1); ret.push_back(0); rep(i,1,p.size()){ rep(_,0,p[i]-p[i-1])ret.push_back(1); ret.push_back(0); } return ret; }; auto decode=[&](vector& q)->vector{ vector ret; int cur=0; for(auto& x:q){ if(x==1)cur++; else{ if(cur)ret.push_back(cur); } } return ret; }; auto hook=[&](vector& p)->Fp{ if(p.empty())return 0; int sum=0; for(auto& x:p)sum+=x; Fp ret=fact.fact(sum); vector rui(p.size(),vector()),add(p.size(),vector()); rep(i,0,p.size()){ rui[i].resize(p[i],1); add[i].resize(p[i],1); for(int j=p[i]-2;j>=0;j--)rui[i][j]+=rui[i][j+1]; } rep(i,0,p.size()-1){ rep(j,0,p[i])add[i+1][j]+=add[i][j]; } rep(i,0,p.size())rep(j,0,p[i])ret*=fact.inv(rui[i][j]+add[i][j]-1); return ret; }; auto maya=encode(a); vector E,O; rep(i,0,maya.size()){ if(i&1)O.push_back(maya[i]); else E.push_back(maya[i]); } auto even=decode(E); auto odd=decode(O); int esum=0,osum=0; for(auto& x:even)esum+=x; for(auto& x:odd)osum+=x; Fp ret=hook(even)*hook(odd); ret*=fact.nCr(esum+osum,esum); io.write(ret.v); return 0; }