import java.util.*;

class Main{
    public static void main(String[] args){
        
        Scanner sc = new Scanner(System.in);

        int N = sc.nextInt();
        int[] H = new int[N];

        if(N==1){
            System.out.println("Yes");
            return;
        }

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

        int N = sc.nextInt();
        int[] H = new int[N];

        if(N==1){
            System.out.println("Yes");
            return;
        }

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

        if(N==1){
            System.out.println("Yes");
            return;
        }

        for(int i=0; i<N; i++){
            H[i] = sc.nextInt();
        }
        
        for(int i=N-1; i>=1; i--){
            if(H[i]+1==H[i-1]){
                H[i - 1] -= 1;
            }
            else if(H[i]+1<H[i-1]){
                System.out.println("No");
                return;
            }
            if(i==1){
                System.out.println("Yes");
            }
        }
    } main {
        
        Scanner sc = new Scanner(System.in);

        int N = sc.nextInt();
        int[] H = new int[N];

        if(N==1){
            System.out.println("Yes");
            return;
        }

        for(int i=0; i<N; i++){
            H[i] = sc.nextInt();
        }
        
        for(int i=N-1; i>=1; i--){
            if(H[i]+1==H[i-1]){
                H[i - 1] -= 1;
            }
            else if(H[i]+1<H[i-1]){
                System.out.println("No");
                return;
            }
            if(i==1){
                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 if(N==1){
            System.out.println("Yes");
            return;
        } N==1 N 1 {
            System.out.println("Yes");
            return;
        } System.out.println("Yes") System.out.println System.out System System.out "Yes" return; 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 for(int i=N-1; i>=1; i--){
            if(H[i]+1==H[i-1]){
                H[i - 1] -= 1;
            }
            else if(H[i]+1<H[i-1]){
                System.out.println("No");
                return;
            }
            if(i==1){
                System.out.println("Yes");
            }
        } int i=N-1; int i=N-1; i N-1 N 1 i>=1 i 1 i-- i-- i {
            if(H[i]+1==H[i-1]){
                H[i - 1] -= 1;
            }
            else if(H[i]+1<H[i-1]){
                System.out.println("No");
                return;
            }
            if(i==1){
                System.out.println("Yes");
            }
        } {
            if(H[i]+1==H[i-1]){
                H[i - 1] -= 1;
            }
            else if(H[i]+1<H[i-1]){
                System.out.println("No");
                return;
            }
            if(i==1){
                System.out.println("Yes");
            }
        } if(H[i]+1==H[i-1]){
                H[i - 1] -= 1;
            }
            else if(H[i]+1<H[i-1]){
                System.out.println("No");
                return;
            } H[i]+1==H[i-1] H[i]+1 H[i] H i 1 H[i-1] H i-1 i 1 {
                H[i - 1] -= 1;
            } H[i - 1] -= 1 H[i - 1] H i - 1 i 1 1 if(H[i]+1<H[i-1]){
                System.out.println("No");
                return;
            } H[i]+1<H[i-1] H[i]+1 H[i] H i 1 H[i-1] H i-1 i 1 {
                System.out.println("No");
                return;
            } System.out.println("No") System.out.println System.out System System.out "No" return; if(i==1){
                System.out.println("Yes");
            } i==1 i 1 {
                System.out.println("Yes");
            } System.out.println("Yes") System.out.println System.out System System.out "Yes" String[] args args
import java.util.*;

class Main{
    public static void main(String[] args){
        
        Scanner sc = new Scanner(System.in);

        int N = sc.nextInt();
        int[] H = new int[N];

        if(N==1){
            System.out.println("Yes");
            return;
        }

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