#include<iostream> #include<vector> #include<string> #include<algorithm> #include<set> #include<queue> using namespace std; using ll = long long; template< typename T > struct BIT2D{ int H,W; vector<vector<T>> data; BIT2D(int h,int w):H(h),W(w),data(h+1,vector<T>(w+1,0)){} void add(int h,int w,T x){ h++;w++; for(int i = h;i<=H;i+=i&(-i)){ for(int j = w;j<=W;j+=j&(-j)){ data[i][j] += x; } } } //sum of [l,r) T sum(int h1,int w1,int h2,int w2){ return sum(h2,w2)-sum(h2,w1-1)-sum(h1-1,w2)+sum(h1-1,w1-1); } T sum(int h,int w){ h++;w++; T now = 0; for(int i = h;i>0;i-=i&(-i)){ for(int j = w;j>0;j-=j&(-j)){ now += data[i][j]; } } return now; } }; int main(){ int n; cin>>n; vector<int> a(n); for(int i = 0;i<n;i++) cin>>a[i]; ll ans = 0; BIT2D<ll> b1(n+2,n+2),b2(n+2,n+2); for(int i = 0;i<n;i++) for(int j = i+1;j<n;j++){ if(a[j]==a[i]+10) { b1.add(i,j,1); } if(a[j]==a[i]+1){ b2.add(i,j,1); } } for(int i = 0;i<n;i++) for(int j = i+2;j<n;j++){ if(a[j]==a[i]+10) { ans += b2.sum(i+1,j+1,j,n); // cout<<i<<" "<<j<<" "<<ans<<endl; } if(a[j]==a[i]+1){ ans += b1.sum(i+1,j+1,j,n); // cout<<i<<" "<<j<<" "<<ans<<endl; } } cout <<ans<<endl; }