N = int(input())
A = list(map(int, input().split()))
for i in range(N):
    if A[i] > 0:
        R = i
A = A[:R+1]
N = len(A)
if N==1:
    if A[0]>1:
        print("No")
        exit()
    else:
        print("Yes")
else:        
    if A[1]>2:
        print("No")
        exit()
    else:
        is_ok = [0 for i in range(N)]
        for i in range(N-1):
            if i==0:
                is_ok[i] = is_ok[i+1] = 1
            else:
                if A[i] +2 == A[i+1] and A[i]<=i+1:
                    is_ok[i] = is_ok[i+1] = 1
        if sum(is_ok) == N:
            print("Yes")
        else:
            print("No")