#include<iostream>
	#include<algorithm>
	#include<vector>
	#include<queue>
	#include<stack>
	#include<list>
	#include<set>
	#include<string>
	using namespace std;
	int gcd(int a, int b) {
		int c = a % b;
		while (c != 0) {
			a = b;
			b = c;
			c = a % b;
		}
		return b;
	}
	struct UnionFind {
		vector<int> par; // par[i]:iの親の番号　(例) par[3] = 2 : 3の親が2

		UnionFind(int N) : par(N) { //最初は全てが根であるとして初期化
			for (int i = 0; i < N; i++) par[i] = i;
		}

		int root(int x) { // データxが属する木の根を再帰で得る：root(x) = {xの木の根}
			if (par[x] == x) return x;
			return par[x] = root(par[x]);
		}

		void unite(int x, int y) { // xとyの木を併合
			int rx = root(x); //xの根をrx
			int ry = root(y); //yの根をry
			if (rx == ry) return; //xとyの根が同じ(=同じ木にある)時はそのまま
			par[rx] = ry; //xとyの根が同じでない(=同じ木にない)時：xの根rxをyの根ryにつける
		}

		bool same(int x, int y) { // 2つのデータx, yが属する木が同じならtrueを返す
			int rx = root(x);
			int ry = root(y);
			return rx == ry;
		}
	};
	typedef long long ll;

	ll M = 1000000007;

	vector<ll> fac(300001); //n!(mod M)
	vector<ll> ifac(300001); //k!^{M-2} (mod M)

	ll mpow(ll x, ll n) {
		ll ans = 1;
		while (n != 0) {
			if (n & 1) ans = ans * x % M;
			x = x * x % M;
			n = n >> 1;
		}
		return ans;
	}
	void setcomb() {
		fac[0] = 1;
		ifac[0] = 1;
		for (ll i = 0; i < 1000000; i++) {
			fac[i + 1] = fac[i] * (i + 1) % M; // n!(mod M)
		}
		ifac[1000000] = mpow(fac[1000000], M - 2);
		for (ll i = 1000000; i > 0; i--) {
			ifac[i - 1] = ifac[i] * i%M;
		}
	}
	ll comb(ll a, ll b) {
		if (a == 0 && b == 0)return 1;
		if (a < b || a < 0)return 0;
		ll tmp = ifac[a - b] * ifac[b] % M;
		return tmp * fac[a] % M;
	}
	ll perm(ll a, ll b) {
		if (a == 0 && b == 0)return 1;
		if (a < b || a < 0)return 0;
		return fac[a] * ifac[a - b] % M;
	}
	// mod. m での a の逆元 a^{-1} を計算する
	long long modinv(long long a) {
		long long b = M, u = 1, v = 0;
		while (b) {
			long long t = a / b;
			a -= t * b; swap(a, b);
			u -= t * v; swap(u, v);
		}
		u %= M;
		if (u < 0) u += M;
		return u;
	}
	vector<vector<ll>> mul(vector<vector<ll>> a, vector<vector<ll>> b, int n) {
		int i, j, k, t;
		vector<vector<ll>> c(n);
		for (i = 0; i < n; i++) {
			for (j = 0; j < n; j++) {
				t = 0;
				for (k = 0; k < n; k++)
					t = (t + a[i][k] * b[k][j] % M) % M;
				c[i].push_back(t);
			}
		}
		return c;
	}

	template< typename Monoid >
	struct SegmentTree {

		int sz;
		vector< Monoid > seg;

		const Monoid M1;

		SegmentTree(int n, const Monoid &M1) : M1(M1) {
			sz = 1;
			while (sz < n) sz <<= 1;
			seg.assign(2 * sz, M1);
		}

		void set(int k, const Monoid &x) {
			seg[k + sz] = x;
		}

		void build() {
			for (int k = sz - 1; k > 0; k--) {
				seg[k] = f(seg[2 * k + 0], seg[2 * k + 1]);
			}
		}

		void update(int k, const Monoid &x) {
			k += sz;
			seg[k] = x;
			while (k >>= 1) {
				seg[k] = f(seg[2 * k + 0], seg[2 * k + 1]);
			}
		}

		Monoid query(int a, int b) {
			Monoid L = M1, R = M1;
			for (a += sz, b += sz; a < b; a >>= 1, b >>= 1) {
				if (a & 1) L = f(L, seg[a++]);
				if (b & 1) R = f(seg[--b], R);
			}
			return f(L, R);
		}

		Monoid value(const int &k) const {
			return seg[k + sz];
		}

		Monoid f(Monoid a, Monoid b) {
			return a + b;
		}
	};

	int main() {
		int n, i, h, p;
		cin >> n;
		cin >> h;
		p = h;
		for (i = 0; i < n - 1; i++) {
			cin >> h;
			if (h < p) {
				cout << "No" << endl;
				return 0;
			}
			if (h > p)
				p = h - 1;
		}
		cout << "Yes" << endl;
	}

Measured memory_bytes: 4992