N=int(input())
A=list(map(int,input().split()))
for i in A:
    if N<i : exit(print("No"))

left,right=[-1 for _ in range(N)],[-1 for _ in range(N)]
n=0
for i in range(N):
    if n<A[i]:
        for j in range(n,A[i]) : left[j]=i
        n=A[i]
n=0
for i in range(N-1,-1,-1):
    if n<A[i]:
        for j in range(n,A[i]) : right[j]=i
        n=A[i]

for i in range(N):
    if N-i<=right[i]-left[i] : exit(print("No"))
print("Yes")