n = int(input())
a = list(map(int, input().split()))

if n == 1:
    print("Yes")
else:
    # Check if all elements are the same and greater than 1
    all_same = True
    first = a[0]
    for num in a[1:]:
        if num != first:
            all_same = False
            break
    if all_same and first > 1:
        print("No")
    else:
        # Check if for any i, a[i] > a[i+1] + 1
        impossible = False
        for i in range(n-1):
            if a[i] > a[i+1] + 1:
                impossible = True
                break
        if impossible:
            print("No")
        else:
            print("Yes")