#include <bits/stdc++.h>
using namespace std;
typedef signed long long ll;

#define _P(...) (void)printf(__VA_ARGS__)
#define FOR(x,to) for(x=0;x<(to);x++)
#define FORR(x,arr) for(auto& x:arr)
#define FORR2(x,y,arr) for(auto& [x,y]:arr)
#define ALL(a) (a.begin()),(a.end())
#define ZERO(a) memset(a,0,sizeof(a))
#define MINUS(a) memset(a,0xff,sizeof(a))
template<class T> bool chmax(T &a, const T &b) { if(a<b){a=b;return 1;}return 0;}
template<class T> bool chmin(T &a, const T &b) { if(a>b){a=b;return 1;}return 0;}
//-------------------------------------------------------

int N;
int A[101010];
unordered_map<int,ll> dp[201010];
ll S[101010];
const ll mo=1000000007;
void solve() {
	int i,j,k,l,r,x,y; string s;
	
	cin>>N;
	S[0]=1;
	for(i=1;i<=N;i++) {
		cin>>x;
		ll sum=0;
		FORR(a,dp[i]) {
			sum+=a.second;
			if(i+a.first<=N) {
				(dp[i+a.first][a.first]+=a.second)%=mo;
			}
		}
		sum+=S[i-1];
		S[i]=sum%mo;
		
		
		if(i==N) cout<<S[i]<<endl;
		
		if(x==1) (dp[i+2][1]+=S[i])%=mo;
		else (dp[i+x][x]+=S[i])%=mo;
		dp[i].clear();
		
	}
	
}


int main(int argc,char** argv){
	string s;int i;
	if(argc==1) ios::sync_with_stdio(false), cin.tie(0);
	FOR(i,argc-1) s+=argv[i+1],s+='\n'; FOR(i,s.size()) ungetc(s[s.size()-1-i],stdin);
	cout.tie(0); solve(); return 0;
}