#include <bits/stdc++.h>
int IntMaxVal = (int)1e20;
int IntMinVal = (int)-1e20;
long long LongMaxVal = (long long)1e20;
long long LongMinVal = (long long)-1e20;
using namespace std;
template <typename T>
struct argument_type;
template <typename T, typename U>
struct argument_type<T(U)> {};
template <typename T1, typename T2>
istream& operator>>(istream& is, pair<T1, T2>& s) {
  is >> s.first >> s.second;
  return is;
}
template <typename T>
ostream& operator<<(ostream& os, const vector<T>& v) {
  for (int i = 0; i < v.size(); i++) os << v[i] << ' ';
  os << '\n';
  ;
  return os;
}
template <typename T1, typename T2>
ostream& operator<<(ostream& s, pair<T1, T2>& t) {
  s << t.first << ' ' << t.second;
  return s;
}
int main() {
  srand(time(NULL));
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int n;
  cin >> n;
  ;
  vector<int> exp(100000 + 1);
  while (n-- > 0) {
    int x;
    cin >> x;
    ;
    int k;
    cin >> k;
    ;
    if (exp[k] == x) {
      exp[k]++;
    } else if (x <= exp[k] - 1) {
    } else {
      cout << "NO";
      return 0;
    }
  }
  cout << "YES";
}
