#include <bits/stdc++.h>
int diru[] = {-1, -1, -1, 0, 0, 1, 1, 1};
int dirv[] = {-1, 0, 1, -1, 1, -1, 0, 1};
using namespace std;
template <class T>
T sq(T n) {
  return n * n;
}
template <class T>
T gcd(T a, T b) {
  return (b != 0 ? gcd<T>(b, a % b) : a);
}
template <class T>
T lcm(T a, T b) {
  return (a / gcd<T>(a, b) * b);
}
template <class T>
bool inside(T a, T b, T c) {
  return a <= b && b <= c;
}
template <class T>
void setmax(T &a, T b) {
  if (a < b) a = b;
}
template <class T>
void setmin(T &a, T b) {
  if (b < a) a = b;
}
template <class T>
T power(T N, T P) {
  return (P == 0) ? 1 : N * power(N, P - 1);
}
int main() {
  int t, q, i, j, n, n1, n2;
  while (scanf("%d", &n) == 1) {
    set<int> s[100005];
    int f = 1;
    for (i = 0; i < n; i++) {
      scanf("%d", &n1);
      scanf("%d", &n2);
      if (n1 > 0 && s[n2].find(n1 - 1) == s[n2].end())
        f = 0;
      else
        s[n2].insert(n1);
    }
    if (f)
      printf("YES\n");
    else
      printf("NO\n");
  }
  return 0;
}
