#include <bits/stdc++.h>   using namespace std;   const long long MOD = 1000000007;   bool used[123456];   bool cmp(const vector<int>& a, const vector<int>& b) {     return a.size() < b.size();   }   int main() {     int n;     cin >> n;     vector<int> p(n + 1);     for (int i = 1; i <= n; ++i) cin >> p[i];     vector<vector<int> > circle;     for (int i = 1; i <= n; ++i) {       if (!used[i]) {         used[i] = 1;         int curi = i;         circle.push_back(vector<int>(1, i));         while (!used[p[curi]]) {           curi = p[curi];           circle.back().push_back(curi);           used[curi] = true;         }       }     }     bool ok = false;     for (int i = 0; i < circle.size(); ++i)       ok |= (circle[i].size() == 2 || circle[i].size() == 1);     if (!ok) {       cout <<  NO ;       return 0;     }     sort(circle.begin(), circle.end(), cmp);     if (circle[0].size() == 1) {       cout <<  YES n ;       for (int i = 1; i < circle.size(); ++i)         for (int j = 0; j < circle[i].size(); ++j)           cout << circle[0][0] <<     << circle[i][j] <<   n ;       return 0;     }     for (int i = 0; i < circle.size(); ++i) {       if (circle[i].size() % 2 != 0) {         cout <<  NO ;         return 0;       }     }     cout <<  YES n ;     cout << circle[0][1] <<     << circle[0][0] <<   n ;     for (int i = 1; i < circle.size(); ++i)       for (int j = 0; j < circle[i].size(); ++j)         cout << circle[0][j % 2] <<     << circle[i][j] <<   n ;   }   