#include <iostream>
#include <cstdio>
#include <cmath>
#include <ctime>
#include <cstdlib>
#include <cassert>
#include <vector>
#include <list>
#include <stack>
#include <queue>
#include <deque>
#include <map>
#include <set>
#include <bitset>
#include <string>
#include <algorithm>
#include <utility>
#include <complex>
#define rep(x, s, t) for(llint (x) = (s); (x) <= (t); (x)++)
#define chmin(x, y) (x) = min((x), (y))
#define chmax(x, y) (x) = max((x), (y))
#define all(x) (x).begin(),(x).end()
#define inf 1e18
#define mod 1000000007

using namespace std;

typedef long long llint;
typedef long long ll;
typedef pair<llint, llint> P;

const ll B = 320;
ll n;
ll a[100005];
ll dp[100005];
ll sum[B][100005];

int main(void)
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	
	cin >> n;
	rep(i, 1, n) cin >> a[i];
	
	dp[1] = 1;
	rep(i, 1, n){
		
		if(i > 1){
			if(a[i-1] != 1) dp[i] = dp[i-1];
			rep(j, 1, B-1) if(i-j >= 1) dp[i] += sum[j][i-j];
			dp[i] %= mod;
		}
		rep(j, 1, B-1){
			ll s = 0;
			if(i-j >= 1) s = sum[j][i-j];
			sum[j][i] = s;
			if(j == a[i]) sum[j][i] += dp[i];
			if(sum[j][i] >= mod) sum[j][i] -= mod;
		}
		
		if(a[i] >= B){
			return -1;
			rep(j, 1, n){
				if(i+j*a[i] > n) break;
				dp[i+j*a[i]] += dp[i];
				if(dp[i+j*a[i]] >= mod) dp[i+j*a[i]] -= mod;
			}
		}
	}
	cout << dp[n] << endl;
	
	/*rep(i, 1, n) cout << sum[1][i] << " "; cout << endl;
	rep(i, 1, n) cout << sum[2][i] << " "; cout << endl;
	rep(i, 1, n) cout << dp[i] << " "; cout << endl;*/
	
	return 0;
}