import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

public class Main {

	public static void main(String[] args) {
		FastScanner scan = new FastScanner(System.in);
		final int N = scan.nextInt();
		int[] H = new int[N];
		for (int i = 0; i < N; i++) {
			H[i] = scan.nextInt();
		}

		boolean ans = true;
		if (H[0] > 0) {
			H[0]--;
		}
		for (int i = 1; i < N; i++) {
			if (H[i] > H[i - 1]) {
				H[i]--;
			} else if (H[i] < H[i - 1]) {
				ans = false;
				break;
			}
		}
		if (ans) {
			System.out.println("Yes");
		} else {
			System.out.println("No");
		}

	}

	static class FastScanner {
        private BufferedReader reader = null;
        private StringTokenizer tokenizer = null;

        public FastScanner(InputStream in) {
            reader = new BufferedReader(new InputStreamReader(in));
            tokenizer = null;
        }

        public String next() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public String nextLine() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    return reader.readLine();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }

            return tokenizer.nextToken("\n");
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

        public double nextDouble() {
             return Double.parseDouble(next());
         }

        public int[] nextIntArray(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }

        public long[] nextLongArray(int n) {
            long[] a = new long[n];
            for (int i = 0; i < n; i++)
                a[i] = nextLong();
            return a;
        }
    }

} import java.io.BufferedReader; BufferedReader java.io import java.io.IOException; IOException java.io import java.io.InputStream; InputStream java.io import java.io.InputStreamReader; InputStreamReader java.io import java.util.StringTokenizer; StringTokenizer java.util public class Main {

	public static void main(String[] args) {
		FastScanner scan = new FastScanner(System.in);
		final int N = scan.nextInt();
		int[] H = new int[N];
		for (int i = 0; i < N; i++) {
			H[i] = scan.nextInt();
		}

		boolean ans = true;
		if (H[0] > 0) {
			H[0]--;
		}
		for (int i = 1; i < N; i++) {
			if (H[i] > H[i - 1]) {
				H[i]--;
			} else if (H[i] < H[i - 1]) {
				ans = false;
				break;
			}
		}
		if (ans) {
			System.out.println("Yes");
		} else {
			System.out.println("No");
		}

	}

	static class FastScanner {
        private BufferedReader reader = null;
        private StringTokenizer tokenizer = null;

        public FastScanner(InputStream in) {
            reader = new BufferedReader(new InputStreamReader(in));
            tokenizer = null;
        }

        public String next() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public String nextLine() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    return reader.readLine();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }

            return tokenizer.nextToken("\n");
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

        public double nextDouble() {
             return Double.parseDouble(next());
         }

        public int[] nextIntArray(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }

        public long[] nextLongArray(int n) {
            long[] a = new long[n];
            for (int i = 0; i < n; i++)
                a[i] = nextLong();
            return a;
        }
    }

} Main public static void main(String[] args) {
		FastScanner scan = new FastScanner(System.in);
		final int N = scan.nextInt();
		int[] H = new int[N];
		for (int i = 0; i < N; i++) {
			H[i] = scan.nextInt();
		}

		boolean ans = true;
		if (H[0] > 0) {
			H[0]--;
		}
		for (int i = 1; i < N; i++) {
			if (H[i] > H[i - 1]) {
				H[i]--;
			} else if (H[i] < H[i - 1]) {
				ans = false;
				break;
			}
		}
		if (ans) {
			System.out.println("Yes");
		} else {
			System.out.println("No");
		}

	} main {
		FastScanner scan = new FastScanner(System.in);
		final int N = scan.nextInt();
		int[] H = new int[N];
		for (int i = 0; i < N; i++) {
			H[i] = scan.nextInt();
		}

		boolean ans = true;
		if (H[0] > 0) {
			H[0]--;
		}
		for (int i = 1; i < N; i++) {
			if (H[i] > H[i - 1]) {
				H[i]--;
			} else if (H[i] < H[i - 1]) {
				ans = false;
				break;
			}
		}
		if (ans) {
			System.out.println("Yes");
		} else {
			System.out.println("No");
		}

	} FastScanner scan = new FastScanner(System.in); scan new FastScanner(System.in) final int N = scan.nextInt(); N scan.nextInt() scan.nextInt scan int[] H = new int[N]; H new int[N] N for (int i = 0; i < N; i++) {
			H[i] = scan.nextInt();
		} int i = 0; int i = 0; i 0 i < N i N i++ i++ i {
			H[i] = scan.nextInt();
		} {
			H[i] = scan.nextInt();
		} H[i] = scan.nextInt() H[i] H i scan.nextInt() scan.nextInt scan boolean ans = true; ans true if (H[0] > 0) {
			H[0]--;
		} H[0] > 0 H[0] H 0 0 {
			H[0]--;
		} H[0]-- H[0] H 0 for (int i = 1; i < N; i++) {
			if (H[i] > H[i - 1]) {
				H[i]--;
			} else if (H[i] < H[i - 1]) {
				ans = false;
				break;
			}
		} int i = 1; int i = 1; i 1 i < N i N i++ i++ i {
			if (H[i] > H[i - 1]) {
				H[i]--;
			} else if (H[i] < H[i - 1]) {
				ans = false;
				break;
			}
		} {
			if (H[i] > H[i - 1]) {
				H[i]--;
			} else if (H[i] < H[i - 1]) {
				ans = false;
				break;
			}
		} if (H[i] > H[i - 1]) {
				H[i]--;
			} else if (H[i] < H[i - 1]) {
				ans = false;
				break;
			} H[i] > H[i - 1] H[i] H i H[i - 1] H i - 1 i 1 {
				H[i]--;
			} H[i]-- H[i] H i if (H[i] < H[i - 1]) {
				ans = false;
				break;
			} H[i] < H[i - 1] H[i] H i H[i - 1] H i - 1 i 1 {
				ans = false;
				break;
			} ans = false ans false break; if (ans) {
			System.out.println("Yes");
		} else {
			System.out.println("No");
		} ans {
			System.out.println("Yes");
		} System.out.println("Yes") System.out.println System.out System System.out "Yes" {
			System.out.println("No");
		} System.out.println("No") System.out.println System.out System System.out "No" String[] args args static class FastScanner {
        private BufferedReader reader = null;
        private StringTokenizer tokenizer = null;

        public FastScanner(InputStream in) {
            reader = new BufferedReader(new InputStreamReader(in));
            tokenizer = null;
        }

        public String next() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public String nextLine() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    return reader.readLine();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }

            return tokenizer.nextToken("\n");
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

        public double nextDouble() {
             return Double.parseDouble(next());
         }

        public int[] nextIntArray(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }

        public long[] nextLongArray(int n) {
            long[] a = new long[n];
            for (int i = 0; i < n; i++)
                a[i] = nextLong();
            return a;
        }
    } FastScanner private BufferedReader reader = null; reader null private StringTokenizer tokenizer = null; tokenizer null public FastScanner(InputStream in) {
            reader = new BufferedReader(new InputStreamReader(in));
            tokenizer = null;
        } FastScanner {
            reader = new BufferedReader(new InputStreamReader(in));
            tokenizer = null;
        } reader = new BufferedReader(new InputStreamReader(in)) reader new BufferedReader(new InputStreamReader(in)) tokenizer = null tokenizer null InputStream in in public String next() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        } next {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        } if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            } tokenizer == null || !tokenizer.hasMoreTokens() tokenizer == null tokenizer null !tokenizer.hasMoreTokens() tokenizer.hasMoreTokens() tokenizer.hasMoreTokens tokenizer {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            } try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                } catch (IOException e) {
                    throw new RuntimeException(e);
                } IOException e {
                    throw new RuntimeException(e);
                } throw new RuntimeException(e); new RuntimeException(e) {
                    tokenizer = new StringTokenizer(reader.readLine());
                } tokenizer = new StringTokenizer(reader.readLine()) tokenizer new StringTokenizer(reader.readLine()) return tokenizer.nextToken(); tokenizer.nextToken() tokenizer.nextToken tokenizer public String nextLine() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    return reader.readLine();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }

            return tokenizer.nextToken("\n");
        } nextLine {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    return reader.readLine();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }

            return tokenizer.nextToken("\n");
        } if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    return reader.readLine();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            } tokenizer == null || !tokenizer.hasMoreTokens() tokenizer == null tokenizer null !tokenizer.hasMoreTokens() tokenizer.hasMoreTokens() tokenizer.hasMoreTokens tokenizer {
                try {
                    return reader.readLine();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            } try {
                    return reader.readLine();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                } catch (IOException e) {
                    throw new RuntimeException(e);
                } IOException e {
                    throw new RuntimeException(e);
                } throw new RuntimeException(e); new RuntimeException(e) {
                    return reader.readLine();
                } return reader.readLine(); reader.readLine() reader.readLine reader return tokenizer.nextToken("\n"); tokenizer.nextToken("\n") tokenizer.nextToken tokenizer "\n" public long nextLong() {
            return Long.parseLong(next());
        } nextLong {
            return Long.parseLong(next());
        } return Long.parseLong(next()); Long.parseLong(next()) Long.parseLong Long next() next public int nextInt() {
            return Integer.parseInt(next());
        } nextInt {
            return Integer.parseInt(next());
        } return Integer.parseInt(next()); Integer.parseInt(next()) Integer.parseInt Integer next() next public double nextDouble() {
             return Double.parseDouble(next());
         } nextDouble {
             return Double.parseDouble(next());
         } return Double.parseDouble(next()); Double.parseDouble(next()) Double.parseDouble Double next() next public int[] nextIntArray(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        } nextIntArray {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        } int[] a = new int[n]; a new int[n] n for (int i = 0; i < n; i++)
                a[i] = nextInt(); int i = 0; int i = 0; i 0 i < n i n i++ i++ i a[i] = nextInt(); a[i] = nextInt() a[i] a i nextInt() nextInt return a; a int n n public long[] nextLongArray(int n) {
            long[] a = new long[n];
            for (int i = 0; i < n; i++)
                a[i] = nextLong();
            return a;
        } nextLongArray {
            long[] a = new long[n];
            for (int i = 0; i < n; i++)
                a[i] = nextLong();
            return a;
        } long[] a = new long[n]; a new long[n] n for (int i = 0; i < n; i++)
                a[i] = nextLong(); int i = 0; int i = 0; i 0 i < n i n i++ i++ i a[i] = nextLong(); a[i] = nextLong() a[i] a i nextLong() nextLong return a; a int n n public class Main {

	public static void main(String[] args) {
		FastScanner scan = new FastScanner(System.in);
		final int N = scan.nextInt();
		int[] H = new int[N];
		for (int i = 0; i < N; i++) {
			H[i] = scan.nextInt();
		}

		boolean ans = true;
		if (H[0] > 0) {
			H[0]--;
		}
		for (int i = 1; i < N; i++) {
			if (H[i] > H[i - 1]) {
				H[i]--;
			} else if (H[i] < H[i - 1]) {
				ans = false;
				break;
			}
		}
		if (ans) {
			System.out.println("Yes");
		} else {
			System.out.println("No");
		}

	}

	static class FastScanner {
        private BufferedReader reader = null;
        private StringTokenizer tokenizer = null;

        public FastScanner(InputStream in) {
            reader = new BufferedReader(new InputStreamReader(in));
            tokenizer = null;
        }

        public String next() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public String nextLine() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    return reader.readLine();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }

            return tokenizer.nextToken("\n");
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

        public double nextDouble() {
             return Double.parseDouble(next());
         }

        public int[] nextIntArray(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }

        public long[] nextLongArray(int n) {
            long[] a = new long[n];
            for (int i = 0; i < n; i++)
                a[i] = nextLong();
            return a;
        }
    }

} public class Main {

	public static void main(String[] args) {
		FastScanner scan = new FastScanner(System.in);
		final int N = scan.nextInt();
		int[] H = new int[N];
		for (int i = 0; i < N; i++) {
			H[i] = scan.nextInt();
		}

		boolean ans = true;
		if (H[0] > 0) {
			H[0]--;
		}
		for (int i = 1; i < N; i++) {
			if (H[i] > H[i - 1]) {
				H[i]--;
			} else if (H[i] < H[i - 1]) {
				ans = false;
				break;
			}
		}
		if (ans) {
			System.out.println("Yes");
		} else {
			System.out.println("No");
		}

	}

	static class FastScanner {
        private BufferedReader reader = null;
        private StringTokenizer tokenizer = null;

        public FastScanner(InputStream in) {
            reader = new BufferedReader(new InputStreamReader(in));
            tokenizer = null;
        }

        public String next() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public String nextLine() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    return reader.readLine();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }

            return tokenizer.nextToken("\n");
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

        public double nextDouble() {
             return Double.parseDouble(next());
         }

        public int[] nextIntArray(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }

        public long[] nextLongArray(int n) {
            long[] a = new long[n];
            for (int i = 0; i < n; i++)
                a[i] = nextLong();
            return a;
        }
    }

} Main
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

public class Main {

	public static void main(String[] args) {
		FastScanner scan = new FastScanner(System.in);
		final int N = scan.nextInt();
		int[] H = new int[N];
		for (int i = 0; i < N; i++) {
			H[i] = scan.nextInt();
		}

		boolean ans = true;
		if (H[0] > 0) {
			H[0]--;
		}
		for (int i = 1; i < N; i++) {
			if (H[i] > H[i - 1]) {
				H[i]--;
			} else if (H[i] < H[i - 1]) {
				ans = false;
				break;
			}
		}
		if (ans) {
			System.out.println("Yes");
		} else {
			System.out.println("No");
		}

	}

	static class FastScanner {
        private BufferedReader reader = null;
        private StringTokenizer tokenizer = null;

        public FastScanner(InputStream in) {
            reader = new BufferedReader(new InputStreamReader(in));
            tokenizer = null;
        }

        public String next() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public String nextLine() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    return reader.readLine();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }

            return tokenizer.nextToken("\n");
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

        public double nextDouble() {
             return Double.parseDouble(next());
         }

        public int[] nextIntArray(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }

        public long[] nextLongArray(int n) {
            long[] a = new long[n];
            for (int i = 0; i < n; i++)
                a[i] = nextLong();
            return a;
        }
    }

}
