#include <bits/stdc++.h>
// #define int long long

#define F(i, a, b) for (int i = (a); i <= (b); i++)
#define dF(i, a, b) for (int i = (a); i >= (b); i--)
using namespace std;

typedef long long ll;
typedef pair<int, int> pii;
typedef bitset<65> bst;

const int N = 200005, M = (N << 1), inf = 1e16, mod = 1e9 + 7;
int n, pos[N], a[N], gen[N];
vector<int> fr;
bst ept;
int check(uint64_t x) {
    uint64_t seed = x;
    F(i, 1, n) {
        seed ^= seed << 13;
        seed ^= seed >> 7;
        seed ^= seed << 17;
        if (seed % i != gen[i])
            return 0;
    }
    return 1;
}
vector<bst> hcy;
void guess() {
    while (hcy.size() > 64) hcy.pop_back();
    while (hcy.size() < 64) hcy.push_back(ept);
    F(i, 0, 63) {
        int flag = 0;
        F(j, i, 63) 
            if (hcy[j][i]) {
                swap(hcy[j], hcy[i]);
                flag = 1; break;
            }
        if (!flag) {
            fr.push_back(i);
            continue;
        }
        F(j, 0, 63) if (i != j && hcy[j][i])
            hcy[j] ^= hcy[i];
    }
}
signed main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0), cout.tie(0);
    cin >> n;
    F(i, 1, n) {
        cin >> a[i];
        pos[a[i]] = i;
    }
    dF(i, n, 1) {
        gen[i] = pos[i] - 1;
        int x = pos[i];
        swap(pos[i], pos[a[i]]);
        swap(a[i], a[x]);
    }
    bst f[105];
    F(i, 0, 63) f[i][i] = 1;
    F(T, 1, min(70, n)) {
        dF(i, 63, 13) f[i] ^= f[i - 13];
        F(i, 0, 63) f[i] ^= f[i + 7];
        dF(i, 63, 17) f[i] ^= f[i - 17];
        F(i, 0, 63) {
            if (T >> i & 1) break;
            else {
                bst t = f[i];
                t[64] = (gen[T] >> i & 1);
                hcy.push_back(t);
            }
        }
    }
    guess();
    int o = fr.size(), res = 0;
    bst x;
    for (int i = 0; i < 1 << o; ++i) {
        uint64_t res = 0;
        x.reset();
        F(j, 0, o - 1) if (i >> j & 1)
            res |= 1ull << fr[j], x[fr[j]] = 1;
        F(j, 0, 63) if (hcy[j][j]) {
            int fl = hcy[j][64];
            F(k, 0, 64) if (hcy[j][k]) fl ^= x[k];
            if (fl) res |= 1ull << j; 
        }
        if (check(res)) {
            cout << res << endl;
            break;
        }
    }
    return 0;
}