text: #define DEBUG 1
  /**
   * File    : C2.cpp
   * Author  : Kazune Takahashi
   * Created : 8/4/2019, 11:42:15 PM
   * Powered by Visual Studio Code
   */
  #include <iostream>
  #include <iomanip>
  #include <algorithm>
  #include <vector>
  #include <string>
  #include <complex>
  #include <tuple>
  #include <queue>
  #include <stack>
  #include <map>
  #include <set>
  #include <unordered_map>
  #include <unordered_set>
  #include <bitset>
  #include <functional>
  #include <random>
  #include <chrono>
  #include <cctype>
  #include <cassert>
  #include <cmath>
  #include <cstdio>
  #include <cstdlib>
  using namespace std;
  #define maxs(x, y) (x = max(x, y))
  #define mins(x, y) (x = min(x, y))
  using ll = long long;
  class mint
  {
  public:
    static ll MOD;
    ll x;
    mint() : x(0) {}
    mint(ll x) : x(x % MOD) {}
    mint operator-() const { return x ? MOD - x : 0; }
    mint &operator+=(const mint &a)
    {
      if ((x += a.x) >= MOD)
      {
        x -= MOD;
      }
      return *this;
    }
    mint &operator-=(const mint &a) { return *this += -a; }
    mint &operator*=(const mint &a)
    {
      (x *= a.x) %= MOD;
      return *this;
    }
    mint &operator/=(const mint &a)
    {
      mint b{a};
      return *this *= b.power(MOD - 2);
    }
    mint operator+(const mint &a) const { return mint(*this) += a; }
    mint operator-(const mint &a) const { return mint(*this) -= a; }
    mint operator*(const mint &a) const { return mint(*this) *= a; }
    mint operator/(const mint &a) const { return mint(*this) /= a; }
    bool operator<(const mint &a) const { return x < a.x; }
    bool operator==(const mint &a) const { return x == a.x; }
    const mint power(ll N)
    {
      if (N == 0)
      {
        return 1;
      }
      else if (N % 2 == 1)
      {
        return *this * power(N - 1);
      }
      else
      {
        mint half = power(N / 2);
        return half * half;
      }
    }
  };
  ll mint::MOD = 1e9 + 7;
  istream &operator>>(istream &stream, mint &a) { return stream >> a.x; }
  ostream &operator<<(ostream &stream, const mint &a) { return stream << a.x; }
  class combination
  {
  public:
    vector<mint> inv, fact, factinv;
    static int MAX_SIZE;
    combination() : inv(MAX_SIZE), fact(MAX_SIZE), factinv(MAX_SIZE)
    {
      inv[1] = 1;
      for (auto i = 2; i < MAX_SIZE; i++)
      {
        inv[i] = (-inv[mint::MOD % i]) * (mint::MOD / i);
      }
      fact[0] = factinv[0] = 1;
      for (auto i = 1; i < MAX_SIZE; i++)
      {
        fact[i] = mint(i) * fact[i - 1];
        factinv[i] = inv[i] * factinv[i - 1];
      }
    }
    mint operator()(int n, int k)
    {
      if (n >= 0 && k >= 0 && n - k >= 0)
      {
        return fact[n] * factinv[k] * factinv[n - k];
      }
      return 0;
    }
  };
  int combination::MAX_SIZE = 3000010;
  ll gcd(ll x, ll y) { return y ? gcd(y, x % y) : x; }
  // constexpr double epsilon = 1e-10;
  // constexpr ll infty = 1000000000000000LL;
  // constexpr int dx[4] = {1, 0, -1, 0};
  // constexpr int dy[4] = {0, 1, 0, -1};
  void Yes()
  {
    cout << "Yes" << endl;
    exit(0);
  }
  void No()
  {
    cout << "No" << endl;
    exit(0);
  }
  
  int main()
  {
    int N;
    cin >> N;
    vector<int> a(N);
    for (auto i = 0; i < N; i++)
    {
      cin >> a[i];
    }
    int pre = -999;
    for (auto i = 0; i < N; i++)
    {
      if (pre <= a[i] - 1)
      {
        pre = a[i] - 1;
      }
      else if (pre <= a[i])
      {
        pre = a[i];
      }
      else
      {
        No();
      }
    }
    Yes();
  }