import sys
sys.setrecursionlimit(10 ** 6)
n = int(input())
a = list(map(int, input().split()))
a2 = [(a[i], i) for i in range(n - 1)]
a2.sort(reverse=True)
v = [0] * n
v[0] = 1
ans = [0] * (n - 1)
G = [[] for i in range(n)]
for i in range(n - 1):
    if a[a2[i][1]] + i < n:
        ans[a2[i][1]] = i + 1
        G[i].append(i + a2[i][0])
    else:
        exit(print("NO"))
def dfs(now):
    v[now] = 1
    for nex in G[now]:
        dfs(nex)
if all(v for i in range(n)):
    print("YES")
else:
    print("NO")