#include<bits/stdc++.h>
#if __has_include(<atcoder/all>)
#include<atcoder/modint>
#endif
using namespace std;
#define LL(...) ll __VA_ARGS__;lin(__VA_ARGS__)
#define RDVL(T,n,...) vec<T>__VA_ARGS__;fe(refs(__VA_ARGS__),e)e.get().resizes(n);lin(__VA_ARGS__)
#define VL(n,...) RDVL(ll,n,__VA_ARGS__)
#define FO(n) for(ll IJK=n;IJK-->0;)
#define fo(i,...) for(auto[i,i##stop,i##step]=for_range<ll>(0,__VA_ARGS__);i<i##stop;i+=i##step)
#define of(i,...) for(auto[i,i##stop,i##step]=for_range<ll>(1,__VA_ARGS__);i>=i##stop;i+=i##step)
#define fe(a,e,...) for(auto&&__VA_OPT__([)e __VA_OPT__(,__VA_ARGS__]):a)
#define defpp template<ostream&o=cout>void pp(const auto&...a){[[maybe_unused]]const char*c="";((o<<c<<a,c=" "),...);o<<'\n';}void epp(const auto&...a){pp<cerr>(a...);}
#define entry defpp void main();void main2();}int main(){my::io();my::main();}namespace my{
#define use_ml1000000007 using ml=atcoder::modint1000000007;
namespace my{
auto&operator<<(ostream&o,const atcoder::modint1000000007&x){return o<<(int)x.val();}
void io(){cin.tie(nullptr)->sync_with_stdio(0);cout<<fixed<<setprecision(15);}
using ll=long long;
using ui32=uint32_t;
using ui64=uint64_t;
constexpr auto refs(auto&...a){return array{ref(a)...};}
template<class T>constexpr auto for_range(T s,T b){T a=0;if(s)swap(a,b);return array{a-s,b,1-s*2};}
template<class T>constexpr auto for_range(T s,T a,T b,T c=1){return array{a-s,b,(1-s*2)*c};}
void lin(auto&...a){(cin>>...>>a);}
auto ceil(auto x,auto y){if(y<0)x=-x,y=-y;return x<=0?x/y:(x-1)/y+1;}
auto gemin_modulo(auto k,auto r,auto m){return ceil(k-r,m)*m+r;}
auto mod(auto a,auto b){return(a%=b)<0?a+b:a;}
constexpr ui64 kth_root_floor(ui64 a,ll k){
  if (k==1)return a;
  auto within=[&](ui32 x){ui64 t=1;FO(k)if(__builtin_mul_overflow(t,x,&t))return false;return t<=a;};

  ui64 r=0;
  of(i,sizeof(ui32)*CHAR_BIT)if(within(r|(1u<<i)))r|=1u<<i;
  return r;
}
constexpr auto sqrt_floor(auto x){return kth_root_floor(x,2);}
template<class...A>using pack_back_t=tuple_element_t<sizeof...(A)-1,tuple<A...>>;
}
namespace my{
template<class V>concept vectorial=is_base_of_v<vector<typename remove_cvref_t<V>::value_type>,remove_cvref_t<V>>;
template<class V>istream&operator>>(istream&i,vector<V>&v){fe(v,e)i>>e;return i;}
template<class V>constexpr int depth=0;
template<vectorial V>constexpr int depth<V> =depth<typename V::value_type>+1;
template<class T>struct core_t_helper{using type=T;};
template<vectorial V>struct core_t_helper<V>{using type=typename core_t_helper<typename V::value_type>::type;};
template<class T>using core_t=core_t_helper<T>::type;
template<class V>struct vec;
template<int D,class T>struct hvec_helper{using type=vec<typename hvec_helper<D-1,T>::type>;};
template<class T>struct hvec_helper<0,T>{using type=T;};
template<int D,class T>using hvec=hvec_helper<D,T>::type;
template<class V>struct vec:vector<V>{
  static constexpr int D=depth<V>+1;
  using C=core_t<V>;
  using vector<V>::vector;
  vec(const auto&...a)requires(sizeof...(a)>=3){resizes(a...);}
  void resizes(const auto&...a){if constexpr(sizeof...(a)==D)*this=make(a...,C{});else*this=make(a...);}
  static auto make(ll n,const auto&...a){
    if constexpr(sizeof...(a)==1)return vec<C>(n,array{a...}[0]);
    else return vec<decltype(make(a...))>(n,make(a...));
  }
  ll size()const{return vector<V>::size();}
  auto&segment_imos_residue(ll a,ll b,ll r,ll m,C x){
    r=mod(r,m);
    a=gemin_modulo(a,r,m);
    b=gemin_modulo(b,r,m);
    if(a<size())(*this)[a]+=x;
    if(b<size())(*this)[b]-=x;
    return*this;
  }
};
template<class...A>requires(sizeof...(A)>=2)vec(const A&...a)->vec<hvec<sizeof...(A)-2,pack_back_t<A...>>>;
}
namespace my{entry
void main(){
  LL(N);
  VL(N,a);

  use_ml1000000007
  vec dp(N,ml{});
  dp[0]=1;

  ll M=sqrt_floor(N);
  vec su(M,N,ml{}); // modごとのimosテーブル

  fo(i,N){
    fo(j,1,M)if(i>=j)su[j][i]+=su[j][i-j]; // modごとのimos

    // dp[i]に反映.
    fo(j,1,M)dp[i]+=su[j][i];

    // 配る
    if(i+1<N)dp[i+1]+=dp[i];

    // a[i]が小さいならimosテーブルに記録
    // a[i]が大きい(=ステップが大きい)なら直接配って間に合う.
    ll L=(a[i]==1?i+2:i+a[i]);
    if(a[i]<M)su[a[i]].segment_imos_residue(L,N,i,a[i],dp[i]);
    else fo(j,L,N,a[i])dp[j]+=dp[i];
  }

  pp(dp[N-1]);
}}