#include <bits/stdc++.h>
using namespace std;
int main () {
    int N;
    cin >> N;
    int A[10010];
    for (int i = 1; i <= N; i ++) {
        cin >> A[i];
    }
    int ans = 0;
    for (int i = 1; i <= N; i ++) {
        if (A[i] == -1) {
            continue;
        }
        int fl = i;
        ans --;
        while (A[fl] != -1) {
            int fl2 = A[fl];
            A[fl] = -1;
            fl = fl2;
            ans ++;
        }
    }
    cout << (ans % 2 ? -1 : 1) << endl;
}