题解

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int main() {
    int N;
    cin >> N;
    
    vector<int> A(N);
    for (int i = 0; i < N; ++i) {
        cin >> A[i];
    }
    
    vector<int> B(N);
    for (int i = 0; i < N; ++i) {
        cin >> B[i];
    }
    
    vector<int> pos_in_B(N + 1, 0);
    for (int i = 0; i < N; ++i) {
        pos_in_B[B[i]] = i + 1;
    }
    
    for (int i = 0; i < N; ++i) {
        A[i] = pos_in_B[A[i]];
    }
    
    int max_so_far = 0;
    int ans = 0;
    
    for (int a : A) {
        if (a > max_so_far) {
            max_so_far = a;
        } else {
            ans += 1;
        }
    }
    
    cout << ans << endl;
    
    return 0;
}