def main():
    n = int(input())
    A = list(map(int, input().split()))
    l = n
    r = 0
    for i in range(n):
        a = A[i]
        if 1 < a:
            a = a-1
            l = min(l, i-a)
            r = max(r, i+a+1)
    if 0 <= l or r <= n:
        return "Yes"
    else:
        return "No"
print(main())