#include <bits/stdc++.h>
using namespace std;

const int ms = 5e5+5;

int arr[ms];
vector<pair<int, int>> edges;

main() {
  int n;
  cin >> n;
  for(int i = 0; i < n; i++) {
    int u, v;
    cin >> u >> v;
    if(v != n) {
      cout << "NO\n";
      return 0;
    }
    arr[u]++;
  }
  sort(arr, arr+n);
  queue<int> q;
  for(int i = 1; i < n; i++) {
    if(arr[i] == 0) q.push(i);
    else {
      int cur = n;
      for(int j = 1; j < arr[i]; j++) {
        if(q.empty()) {
          cout << "NO\n";
          return 0;
        }
        int u = q.front();
        q.pop();
        edges.emplace_back(cur, u);
      }
      edges.emplace_back(cur, i);
    }
  }
  cout << "YES\n";
  for(auto e : edges) {
    cout << e.first << ' ' << e.second << '\n';
  }
}