#include <bits/stdc++.h>
using namespace std;
typedef int64_t lld;
typedef uint64_t llu;
typedef long double llf;
#define PB push_back
#define ALL(x) begin(x), end(x)
#define WC(x) while(x--)
#define FF first
#define SS second
const int N = 3000000 + 5;

int a[N], b[N], pos[N];

int get_array(int[]);

int main(){
	int n = get_array(a);
	int m = get_array(b);
	if(n != m){
		puts("-1");
		return 0;
	}
	for(int i=0;i<n;i++) pos[b[i]] = i;
	int ans = 0;
	for(int i=0;i<m;i++){
		if(b[i]==a[i]) continue;
		int x = i, y = pos[a[i]];
		pos[b[x]] = y; pos[b[y]] = x;
		swap(b[x], b[y]);
		ans ++;
	}
	printf("%d\n", ans);
	return 0;
}

int get_array(int arr[]){
	int p = 0;
	while(true){
		int x = 0;
		char c = getchar_unlocked();
		if(c == '\n') return 0;
		while(c == ' ') c=getchar_unlocked();
		while(isdigit(c)){
			x = x*10+c-'0';
			c = getchar_unlocked();
		}
		arr[p++] = x;
		if(c == '\n') break;
	}
	return p;
}