#include <stdio.h>
#include <stdlib.h>

int main(int argc, char **argv)
{
  int n, k, i;
  int *odchozi, *prichozi, *precislovani;

  scanf("%d", &n);

  odchozi = (int *) malloc(n*sizeof(int));
  prichozi = (int *) malloc(n*sizeof(int));
  precislovani = (int *) malloc(n*sizeof(int));

  for (i = 0; i < n; i++)
  { scanf("%d", &odchozi[i]); }

  for (i = 0; i < n; i++)
  { scanf("%d", &prichozi[i]); }

  for (i = 0; i < n; i++)
  { precislovani[odchozi[i]] = i; }

  k = 1;
  for (i = 0; i < n-1; i++)
  {
    if (precislovani[prichozi[i+1]] > precislovani[prichozi[i]])
      k++;
    else
      break;
  }

  printf("%d\n", n-k);

  return 0;
}