import java.util.Scanner;
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();
	}
	sc.close();

	for(int i=N-1;i>0;i--) {
		if(H[i]==H[i-1]-1) {
			H[i-1]--;
		}else if(H[i]<H[i-1]-1) {
			System.out.println("No");
			System.exit(0);
		}
	}
	System.out.println("Yes");


}
} import java.util.Scanner; Scanner 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();
	}
	sc.close();

	for(int i=N-1;i>0;i--) {
		if(H[i]==H[i-1]-1) {
			H[i-1]--;
		}else if(H[i]<H[i-1]-1) {
			System.out.println("No");
			System.exit(0);
		}
	}
	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();
	}
	sc.close();

	for(int i=N-1;i>0;i--) {
		if(H[i]==H[i-1]-1) {
			H[i-1]--;
		}else if(H[i]<H[i-1]-1) {
			System.out.println("No");
			System.exit(0);
		}
	}
	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();
	}
	sc.close();

	for(int i=N-1;i>0;i--) {
		if(H[i]==H[i-1]-1) {
			H[i-1]--;
		}else if(H[i]<H[i-1]-1) {
			System.out.println("No");
			System.exit(0);
		}
	}
	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 sc.close() sc.close sc for(int i=N-1;i>0;i--) {
		if(H[i]==H[i-1]-1) {
			H[i-1]--;
		}else if(H[i]<H[i-1]-1) {
			System.out.println("No");
			System.exit(0);
		}
	} int i=N-1; int i=N-1; i N-1 N 1 i>0 i 0 i-- i-- i {
		if(H[i]==H[i-1]-1) {
			H[i-1]--;
		}else if(H[i]<H[i-1]-1) {
			System.out.println("No");
			System.exit(0);
		}
	} {
		if(H[i]==H[i-1]-1) {
			H[i-1]--;
		}else if(H[i]<H[i-1]-1) {
			System.out.println("No");
			System.exit(0);
		}
	} if(H[i]==H[i-1]-1) {
			H[i-1]--;
		}else if(H[i]<H[i-1]-1) {
			System.out.println("No");
			System.exit(0);
		} H[i]==H[i-1]-1 H[i] H i H[i-1]-1 H[i-1] H i-1 i 1 1 {
			H[i-1]--;
		} H[i-1]-- H[i-1] H i-1 i 1 if(H[i]<H[i-1]-1) {
			System.out.println("No");
			System.exit(0);
		} H[i]<H[i-1]-1 H[i] H i H[i-1]-1 H[i-1] H i-1 i 1 1 {
			System.out.println("No");
			System.exit(0);
		} System.out.println("No") System.out.println System.out System System.out "No" System.exit(0) System.exit System 0 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();
	}
	sc.close();

	for(int i=N-1;i>0;i--) {
		if(H[i]==H[i-1]-1) {
			H[i-1]--;
		}else if(H[i]<H[i-1]-1) {
			System.out.println("No");
			System.exit(0);
		}
	}
	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();
	}
	sc.close();

	for(int i=N-1;i>0;i--) {
		if(H[i]==H[i-1]-1) {
			H[i-1]--;
		}else if(H[i]<H[i-1]-1) {
			System.out.println("No");
			System.exit(0);
		}
	}
	System.out.println("Yes");


}
} Main
import java.util.Scanner;
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();
	}
	sc.close();

	for(int i=N-1;i>0;i--) {
		if(H[i]==H[i-1]-1) {
			H[i-1]--;
		}else if(H[i]<H[i-1]-1) {
			System.out.println("No");
			System.exit(0);
		}
	}
	System.out.println("Yes");


}
}
