import java.util.*;
public class Main {
	public static void main(String args[]) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int H[] = new int[N];
		for(int i = 0; i < N; i++) {
			H[i] = sc.nextInt();
		}
		
		int height = Integer.MAX_VALUE;
		for(int i = N - 1; i >= 0; i--) {
			if(height < H[i]) {
				if(height == H[i] - 1) {
					height = H[i] - 1;
				} else {
					System.out.println("No");
					return;
				}
			} else {
				height = H[i];
			}
		}
		System.out.println("Yes");
	}
} import java.util.*; util.* java public class Main {
	public static void main(String args[]) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int H[] = new int[N];
		for(int i = 0; i < N; i++) {
			H[i] = sc.nextInt();
		}
		
		int height = Integer.MAX_VALUE;
		for(int i = N - 1; i >= 0; i--) {
			if(height < H[i]) {
				if(height == H[i] - 1) {
					height = H[i] - 1;
				} else {
					System.out.println("No");
					return;
				}
			} else {
				height = H[i];
			}
		}
		System.out.println("Yes");
	}
} Main public static void main(String args[]) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int H[] = new int[N];
		for(int i = 0; i < N; i++) {
			H[i] = sc.nextInt();
		}
		
		int height = Integer.MAX_VALUE;
		for(int i = N - 1; i >= 0; i--) {
			if(height < H[i]) {
				if(height == H[i] - 1) {
					height = H[i] - 1;
				} else {
					System.out.println("No");
					return;
				}
			} else {
				height = H[i];
			}
		}
		System.out.println("Yes");
	} main {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int H[] = new int[N];
		for(int i = 0; i < N; i++) {
			H[i] = sc.nextInt();
		}
		
		int height = Integer.MAX_VALUE;
		for(int i = N - 1; i >= 0; i--) {
			if(height < H[i]) {
				if(height == H[i] - 1) {
					height = H[i] - 1;
				} else {
					System.out.println("No");
					return;
				}
			} else {
				height = H[i];
			}
		}
		System.out.println("Yes");
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int N = sc.nextInt(); N sc.nextInt() sc.nextInt sc int H[] = new int[N]; H new int[N] N for(int i = 0; i < N; i++) {
			H[i] = sc.nextInt();
		} int i = 0; int i = 0; i 0 i < N i N i++ i++ i {
			H[i] = sc.nextInt();
		} {
			H[i] = sc.nextInt();
		} H[i] = sc.nextInt() H[i] H i sc.nextInt() sc.nextInt sc int height = Integer.MAX_VALUE; height Integer.MAX_VALUE Integer Integer.MAX_VALUE for(int i = N - 1; i >= 0; i--) {
			if(height < H[i]) {
				if(height == H[i] - 1) {
					height = H[i] - 1;
				} else {
					System.out.println("No");
					return;
				}
			} else {
				height = H[i];
			}
		} int i = N - 1; int i = N - 1; i N - 1 N 1 i >= 0 i 0 i-- i-- i {
			if(height < H[i]) {
				if(height == H[i] - 1) {
					height = H[i] - 1;
				} else {
					System.out.println("No");
					return;
				}
			} else {
				height = H[i];
			}
		} {
			if(height < H[i]) {
				if(height == H[i] - 1) {
					height = H[i] - 1;
				} else {
					System.out.println("No");
					return;
				}
			} else {
				height = H[i];
			}
		} if(height < H[i]) {
				if(height == H[i] - 1) {
					height = H[i] - 1;
				} else {
					System.out.println("No");
					return;
				}
			} else {
				height = H[i];
			} height < H[i] height H[i] H i {
				if(height == H[i] - 1) {
					height = H[i] - 1;
				} else {
					System.out.println("No");
					return;
				}
			} if(height == H[i] - 1) {
					height = H[i] - 1;
				} else {
					System.out.println("No");
					return;
				} height == H[i] - 1 height H[i] - 1 H[i] H i 1 {
					height = H[i] - 1;
				} height = H[i] - 1 height H[i] - 1 H[i] H i 1 {
					System.out.println("No");
					return;
				} System.out.println("No") System.out.println System.out System System.out "No" return; {
				height = H[i];
			} height = H[i] height H[i] H i System.out.println("Yes") System.out.println System.out System System.out "Yes" String args[] args public class Main {
	public static void main(String args[]) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int H[] = new int[N];
		for(int i = 0; i < N; i++) {
			H[i] = sc.nextInt();
		}
		
		int height = Integer.MAX_VALUE;
		for(int i = N - 1; i >= 0; i--) {
			if(height < H[i]) {
				if(height == H[i] - 1) {
					height = H[i] - 1;
				} else {
					System.out.println("No");
					return;
				}
			} else {
				height = H[i];
			}
		}
		System.out.println("Yes");
	}
} public class Main {
	public static void main(String args[]) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int H[] = new int[N];
		for(int i = 0; i < N; i++) {
			H[i] = sc.nextInt();
		}
		
		int height = Integer.MAX_VALUE;
		for(int i = N - 1; i >= 0; i--) {
			if(height < H[i]) {
				if(height == H[i] - 1) {
					height = H[i] - 1;
				} else {
					System.out.println("No");
					return;
				}
			} else {
				height = H[i];
			}
		}
		System.out.println("Yes");
	}
} Main
import java.util.*;
public class Main {
	public static void main(String args[]) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int H[] = new int[N];
		for(int i = 0; i < N; i++) {
			H[i] = sc.nextInt();
		}
		
		int height = Integer.MAX_VALUE;
		for(int i = N - 1; i >= 0; i--) {
			if(height < H[i]) {
				if(height == H[i] - 1) {
					height = H[i] - 1;
				} else {
					System.out.println("No");
					return;
				}
			} else {
				height = H[i];
			}
		}
		System.out.println("Yes");
	}
}
