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))