#include <iostream>
#include <cmath>
#include <cstdio>
#include <algorithm>
#include <string>
#include <vector>
#include <queue>
#include <string.h>
#include <map>
#include <fstream>
#include <functional>
#include <bitset>
#include <iomanip>
#include <stack>
#include <set>
#include <climits>
#define MAX_N 200010
#define PI 3.141592653589
#define ESP 1e-20
#define BS 10
#define MOD 1000000007 
#define ZERO 10001
#define YJSNPI 810
#define INF (1LL << 50)
#define ADD(a, b) a = (a + (ll)b) % MOD
#define MUL(a, b) a = (a * (ll)b) % MOD
#define MAX(a, b) a = max(a, b)
#define MIN(a, b) a = min(a, b)

using namespace std;

typedef pair<int, int> pi;
typedef long long ll;

int N;
int goal[100], rev[100], ans[100];

bool loop(int at) {
	/*
	cout << at << " ";
	for(int i = 0; i < N; i++) {
		cout << ans[i] << " ";
	}
	cout << endl;
	*/
	if(ans[at] == -1) {
		for(int i = 0; i < N; i++) {
			ans[at] = i;
			if(ans[i] == -1) ans[i] = rev[at];
			else if(ans[i] != rev[at]) {
				ans[at] = -1; continue;
			}
			if(loop(i)) return true;
			ans[at] = -1;
			ans[i] = -1;
		}
	}
	else {
		if(ans[ans[at]] == -1) {
			ans[ans[at]] = rev[at];
			if(loop(ans[ans[at]])) return true;
			ans[ans[at]] = -1;
			return false;
		}
		if(goal[ans[ans[at]]] != at) return false;
		bool found = false;
		for(int i = 0; i < N; i++) {
			if(ans[i] == -1) {
				if(loop(i)) return true;
				found = true;
				break;
			}
		}
		if(found) return false;
		else {
			for(int i = 0; i < N; i++) {
				if(goal[ans[ans[i]]] != i) return false;
			}
			return true;
		}
	}
	return false;
}

int main() {
	cin >> N;
	for(int i = 0; i < N; i++) {
		cin >> goal[i]; goal[i]--;
		rev[goal[i]] = i;
	}
	/*
	for(int i = 0; i < N; i++) {
		cout << rev[i] << " ";
	}
	cout << endl;
	*/
	memset(ans, -1, sizeof(ans));
	if(loop(0)) cout << "Yes" << endl;
	else cout << "No" << endl;
}