#include <iostream>
#include <iomanip>
#include <sstream>
#include <vector>
#include <string>
#include <set>
#include <unordered_set>
#include <map>
#include <unordered_map>
#include <stack>
#include <queue>
#include <deque>
#include <algorithm>
#include <functional>
#include <iterator>
#include <limits>
#include <numeric>
#include <utility>
#include <cmath>
#include <cassert>
#include <cstdio>

using namespace std; using namespace placeholders;

typedef long long LL;
typedef unsigned long long ULL;
typedef vector< int > VI;
typedef vector< vector< int > > VVI;
typedef vector< string > VS;
typedef stringstream SS;
typedef pair< int, int > PII;
typedef vector< pair< int, int > > VPII;
#define VT( T ) vector< T >
#define VVT( T ) vector< vector< T > >
#define LIM( T ) numeric_limits< T >

template < typename T > inline istream& operator>>( istream &s, vector< T > &v ){ for ( T &t : v ) { s >> t; } return s; }
template < typename T > inline ostream& operator<<( ostream &s, const vector< T > &v ){ for ( int i = 0; i < int( v.size() ); ++i ){ s << ( " " + !i ) << v[i]; } return s; }
template < typename T > inline T fromString( const string &s ) { T res; istringstream iss( s ); iss >> res; return res; };
template < typename T > inline string toString( const T &a ) { ostringstream oss; oss << a; return oss.str(); };

#define REP2( i, n ) REP3( i, 0, n )
#define REP3( i, m, n ) for ( int i = ( int )( m ); i < ( int )( n ); ++i )
#define GET_REP( a, b, c, F, ... ) F
#define REP( ... ) GET_REP( __VA_ARGS__, REP3, REP2 )( __VA_ARGS__ )
#define FOR( e, c ) for ( auto &e : c )
#define ALL( c ) ( c ).begin(), ( c ).end()
#define AALL( a, t ) ( t* )a, ( t* )a + sizeof( a ) / sizeof( t )
#define DRANGE( c, p ) ( c ).begin(), ( c ).begin() + p, ( c ).end()

#define SZ( v ) ( (int)( v ).size() )
#define PB push_back
#define EM emplace
#define EB emplace_back
#define BI back_inserter

#define EXIST( c, e ) ( ( c ).find( e ) != ( c ).end() )

#define MP make_pair
#define fst first
#define snd second

#define DUMP( x ) cerr << #x << " = " << ( x ) << endl

constexpr int INF = LIM( int )::max();

int main()
{
	cin.tie( 0 );
	ios::sync_with_stdio( false );

	for ( int N; cin >> N && N; )
	{
		VI ps( N );
		cin >> ps;

		VI distances( N, INF );
		distances[0] = 0;

		queue< int > que;
		que.push( 0 );

		VI jump( N, -1 );

		while ( !que.empty() )
		{
			const int cur = que.front();
			que.pop();

			REP( i, 1, 7 )
			{
				bool ok = true;
				int nex = cur + i;
				
				if ( N <= nex )
				{
					break;
				}

				if ( ps[ nex ] == 0 )
				{
				}
				else if ( jump[ nex ] == -2 )
				{
					ok = false;
				}
				else if ( jump[ nex ] != -1 )
				{
					nex = jump[ nex ];
				}
				else
				{
					set< int > visited;
					while ( ps[ nex ] )
					{
						visited.insert( nex );
						nex += ps[ nex ];

						if ( EXIST( visited, nex ) )
						{
							ok = false;
							break;
						}
					}

					FOR( vis, visited )
					{
						jump[ vis ] = ok ? nex : -2;
					}
				}

				if ( ok && distances[ cur ] + 1 < distances[ nex ] )
				{
					distances[ nex ] = distances[ cur ] + 1;
					que.push( nex );
				}
			}
		}

		cout << distances.back() << endl;
	}

	return 0;
}

Measured memory_bytes: 6012