#include <vector>
#include <list>
#include <map>
#include <set>
#include <stack>
#include <queue>
#include <deque>
#include <algorithm>
#include <utility>
#include <functional>
#include <sstream>
#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <climits>
#include <cassert>
using namespace std;
inline int toInt(string s) {int v; istringstream sin(s);sin>>v;return v;}
template<class T> inline string toString(T x) {ostringstream sout;sout<<x;return sout.str();}
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<string> vs;
typedef pair<int, int> pii;
typedef long long ll;
#define ALL(a) (a).begin(),(a).end()
#define RALL(a) (a).rbegin(),(a).rend()
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n) FOR(i,0,n)
const double EPS = 1e-9;
const double PI  = acos(-1.0);

int main(){
	int n;
	cin>>n;
	vi p(n);
	REP(i,n){
		cin>>p[i];
	}
	queue<int> q;
	vi cost(n,-1);
	q.push(0);
	cost[0]=0;
	while(q.size()){
		int cur=q.front();q.pop();
		FOR(die,1,6+1){
			int pos=cur+die;
			if(pos>=n)continue;
			while(cost[pos]==-1&&p[pos]!=0){
				cost[pos]=cost[cur]+1;
				pos+=p[pos];
			}
			if(p[pos]==0&&cost[pos]==-1){
				cost[pos]=cost[cur]+1;
				q.push(pos);
			}
		}
	}
	cout<<cost[n-1]<<endl;
}