N = int(input())
A = list(map(int, input().split()))

segments = []
current_segment = []
for num in A:
    if num == 0:
        if current_segment:
            segments.append(current_segment)
            current_segment = []
    else:
        current_segment.append(num)
if current_segment:
    segments.append(current_segment)

valid = True
for seg in segments:
    m = len(seg)
    if m == 0:
        continue
    if seg[0] != 1 or seg[-1] != 1:
        valid = False
        break
    # Check left to right
    for i in range(1, m):
        if seg[i] > seg[i-1] + 1:
            valid = False
            break
    if not valid:
        break
    # Check right to left
    for i in range(m-2, -1, -1):
        if seg[i] > seg[i+1] + 1:
            valid = False
            break
    if not valid:
        break

print("Yes" if valid else "No")