#include <bits/stdc++.h>
using namespace std;
int in[100005];
int in2[100005];
int remlocate[100005];
int main() {
  int n;
  cin >> n;
  for (int i = 0; i < n; ++i) {
    cin >> in[i];
  }
  for (int i = 0; i < n; ++i) {
    cin >> in2[i];
    remlocate[in2[i]] = i;
  }
  int go1 = n - 1;
  int go2 = n - 1;
  int cnt = 0;
  for (int i = 0; i < n; ++i) {
    while (in2[go2] == 0) {
      go2--;
    }
    if (in[go1] != in2[go2]) {
      cnt++;
      in2[remlocate[in[go1]]] = 0;
      go1--;
    } else {
      go1--;
      go2--;
    }
  }
  cout << cnt << endl;
  return 0;
}
