In a recent study of the tree line, or someone else with the current board

#define ll long long
#define LL(x) (x<<1)
#define RR(x) (x<<1|1)
#define MID(a,b) (a+((b-a)>>1))
#define inf 0x7f7f7f7f
const int N=5005;
int a[5005];
struct node
  {
      int lft,rht;
      int sum;
      int mid()
      {
          return MID(lft,rht);
      }
  };

struct Segtree
  {
      node tree[N*4];
      void build(int lft,int rht,int rt)
      {
          tree[rt].lft=lft;
          tree[rt].rht=rht;
          tree[rt].sum=0;
          if(lft!=rht)
          {
              int mid=tree[rt].mid();
              build(lft,mid,LL(rt));
              build(mid+1,rht,RR(rt));
              tree[rt].sum=tree[LL(rt)].sum+tree[RR(rt)].sum;
         }
      }
      void updata(int pos,int rt)
      {
          if(tree[rt].lft==tree[rt].rht)
              tree[rt].sum++;
          else
          {
              int mid=tree[rt].mid();
              if(pos<=mid)
                  updata(pos,LL(rt));
              else
                  updata(pos,RR(rt));
              tree[rt].sum=tree[LL(rt)].sum+tree[RR(rt)].sum;
          }
      }
      int query(int st,int ed,int rt)
      {
          int lft=tree[rt].lft,rht=tree[rt].rht;
          if(st<=lft&&rht<=ed){
    return tree[rt].sum;
    }
          else
          {
              int mid=tree[rt].mid();
              int sum1=0,sum2=0;
             if(st<=mid)
                  sum1=query(st,ed,LL(rt));
              if(ed>mid)
                  sum2=query(st,ed,RR(rt));
                  return sum1+sum2;
          }
      }
  }seg;