def main(n,a):
  mod=10**9+7
  dp=[0]*(n+1)
  dp[1]=1
  for i in range(1,n):
    if dp[i]==0:continue
    x=a[i-1]
    dp[i+1]+=dp[i]
    dp[i+1]%=mod
    now=i+x
    if now==i+1:now+=1
    while now<=n:
      dp[now]+=dp[i]
      dp[now]%=mod
      now+=x
  return dp[n]
n=int(input())
a=list(map(int,input().split()))
print(main(n,a))