#line 2 "cpplib/util/template.hpp" #pragma GCC optimize("Ofast") #pragma GCC optimize("unroll-loops") #pragma GCC target("avx2") #include using namespace std; struct __INIT__{__INIT__(){cin.tie(0);ios::sync_with_stdio(false);cout< vec; typedef vector> mat; typedef vector>> mat3; typedef vector svec; typedef vector> smat; templateusing V=vector; templateusing VV=V>; templateinline void output(T t){bool f=0;for(auto i:t){cout<<(f?" ":"")<inline void output2(T t){for(auto i:t)output(i);} templateinline void debug(T t){bool f=0;for(auto i:t){cerr<<(f?" ":"")<inline void debug2(T t){for(auto i:t)output(i);} #define loop(n) for(long long _=0;_<(long long)(n);++_) #define _overload4(_1,_2,_3,_4,name,...) name #define __rep(i,a) repi(i,0,a,1) #define _rep(i,a,b) repi(i,a,b,1) #define repi(i,a,b,c) for(long long i=(long long)(a);i<(long long)(b);i+=c) #define rep(...) _overload4(__VA_ARGS__,repi,_rep,__rep)(__VA_ARGS__) #define _overload3_rev(_1,_2,_3,name,...) name #define _rep_rev(i,a) repi_rev(i,0,a) #define repi_rev(i,a,b) for(long long i=(long long)(b)-1;i>=(long long)(a);--i) #define rrep(...) _overload3_rev(__VA_ARGS__,repi_rev,_rep_rev)(__VA_ARGS__) // #define rep(i,...) for(auto i:range(__VA_ARGS__)) // #define rrep(i,...) for(auto i:reversed(range(__VA_ARGS__))) // #define repi(i,a,b) for(lint i=lint(a);i<(lint)(b);++i) // #define rrepi(i,a,b) for(lint i=lint(b)-1;i>=lint(a);--i) // #define irep(i) for(lint i=0;;++i) // inline vector range(long long n){if(n<=0)return vector();vectorv(n);iota(v.begin(),v.end(),0LL);return v;} // inline vector range(long long a,long long b){if(b<=a)return vector();vectorv(b-a);iota(v.begin(),v.end(),a);return v;} // inline vector range(long long a,long long b,long long c){if((b-a+c-1)/c<=0)return vector();vectorv((b-a+c-1)/c);for(int i=0;i<(int)v.size();++i)v[i]=i?v[i-1]+c:a;return v;} // templateinline T reversed(T v){reverse(v.begin(),v.end());return v;} #define all(n) begin(n),end(n) templatebool chmin(T& s,const E& t){bool res=s>t;s=min(s,t);return res;} templatebool chmax(T& s,const E& t){bool res=s(s,t);return res;} const vector dx={1,0,-1,0,1,1,-1,-1}; const vector dy={0,1,0,-1,1,-1,1,-1}; #define SUM(v) accumulate(all(v),0LL) templateauto make_vector(T x,int arg,Args ...args){if constexpr(sizeof...(args)==0)return vector(arg,x);else return vector(arg,make_vector(x,args...));} #define extrep(v,...) for(auto v:__MAKE_MAT__({__VA_ARGS__})) #define bit(n,a) ((n>>a)&1) vector> __MAKE_MAT__(vector v){if(v.empty())return vector>(1,vector());long long n=v.back();v.pop_back();vector> ret;vector> tmp=__MAKE_MAT__(v);for(auto e:tmp)for(long long i=0;i>; templateusing graph_w=vector>>; templateostream& operator<<(ostream& out,pairv){out<<"("< struct maybe{ bool _is_none; T val; maybe():_is_none(true){} maybe(T val):_is_none(false),val(val){} T unwrap()const{ assert(!_is_none); return val; } T unwrap_or(T e)const{ return _is_none?e:val; } bool is_none()const{return _is_none;} bool is_some()const{return !_is_none;} }; template auto expand(F op){ return [&op](const maybe& s,const maybe& t){ if(s.is_none())return t; if(t.is_none())return s; return maybe(op(s.unwrap(),t.unwrap())); }; } #line 4 "cpplib/segment_tree/segment_tree.hpp" /** * @brief セグメント木 * @see https://en.wikipedia.org/wiki/Segment_tree */ template class segment_tree{ maybe* node; F op; int n=1; public: segment_tree(){} segment_tree(int sz,F op=F()):op(op){ while(n<=sz)n<<=1; node=new maybe[n*2]; for(int i=0;i(); } segment_tree(const std::vector&v,F op=F()):op(op){ auto f=expand(op); const int sz=v.size(); while(n<=sz)n<<=1; node=new maybe[n*2](); for(int i=0;i(v[i]); for(int i=n-1;i>=1;i--)node[i]=f(node[i*2],node[i*2+1]); } maybe get(int l,int r){ auto f=expand(op); l+=n;r+=n; maybe s,t; while(l>=1;r>>=1; } return f(s,t); } void apply(int t,T _val){ auto f=expand(op); t+=n; maybe val=maybe(_val); while(t){ node[t]=f(node[t],val); t=t>>1; } } void apply_left(int t,T _val){ auto f=expand(op); t+=n; maybe val=maybe(_val); while(t){ node[t]=f(val,node[t]); t=t>>1; } } void change(int t,T val){ auto f=expand(op); t+=n; node[t]=maybe(val); while(t>1){ t=t>>1; node[t]=f(node[t*2],node[t*2+1]); } } }; #line 3 "main.cpp" int main(){ lint n; cin>>n; vec a(n); rep(i,n)cin>>a[i]; vec v(n); rep(i,n)v[a[i]-1]=i; segment_tree>seg(n); lint ans=0; rep(i,n){ ans+=seg.get(v[i],n).unwrap_or(0); seg.apply(v[i],1); } cout<