Toph(E) set using upper_bound

#include<bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>
using namespace std;
using namespace __gnu_pbds;
using ll = long long;
#define pb push_back
#define ff first
#define ss second

template <typename T>  using orderedSet =
   tree<T, null_type, less<T>,
   rb_tree_tag, tree_order_statistics_node_update>;

int main()
{
    int n;
    scanf("%d",&n);
    int a[n+5],b[n+5];

    for(int i=1; i<=n; i++)
        scanf("%d",&a[i]);
    int pos[n+5];
    for(int i=1; i<=n; i++)
    {
        scanf("%d",&b[i]);
        pos[b[i]]=i;
    }

    int ans=0;
    orderedSet<int>st;
    st.insert(0);
    for(int i=1; i<=n; i++)
    {
        int x=pos[a[i]];

        auto p=st.upper_bound(x);
        int z=st.order_of_key(*p);
        if(z==0)
            st.insert(x);
        else
        {
            int y=st.size()-z;
            ans+=y;
            //cout<<a[i]<<": "<<st.size()<<" "<<z<<endl;
            st.insert(x);
        }
    }

    printf("%d",ans);

    return 0;
}