import java.io.*;
import java.util.*;

public class Main {

    static int N;
    static int[] P;

    public static void main(String[] args) {
        FastScanner sc = new FastScanner(System.in);
        N = sc.nextInt();
        P = sc.nextIntArray(N);

        System.out.println(solve());
    }

    static int solve() {
        // 踏んだマス -> 止まるマス
        int[] D = new int[N];
        int INF = -1;
        int EMP = -2;
        Arrays.fill(D, EMP);
        for (int i = 0; i < N; i++) {
            if( D[i] != EMP ) {
                continue;
            }

            if( P[i] == 0 ) {
                D[i] = i;
                continue;
            }

            Set<Integer> path = new HashSet<>();
            int curr = i;
            path.add(curr);
            while(true) {
                int p = P[curr];

                if( p == 0 ) {
                    for (Integer each : path) D[each] = curr;
                    break;
                }

                int next = curr + p;
                if( path.contains(next) ) {
                    for (Integer each : path) D[each] = INF;
                    break;
                }

                curr = next;
                path.add(curr);
            }
        }
        // debug(D);

        List<Edge> E = new ArrayList<>();
        for (int i = 0; i < N; i++) {
            if( D[i] != i ) continue;

            // [+1, +6]
            for (int sai = 1; sai <= 6; sai++) {
                int j = i + sai;
                if( j >= N ) break;
                if( D[j] == -1 ) continue;

                E.add( new Edge(i, D[j]) );
            }
        }

        int[][] G = adjD(N, E);

        int[] dist = new int[N];
        Arrays.fill(dist, Integer.MAX_VALUE);
        ArrayDeque<Integer> q = new ArrayDeque<>();
        q.add( 0 );
        dist[0] = 0;

        while(!q.isEmpty()) {
            Integer a = q.poll();
            for (int b : G[a]) {
                if( dist[b] > dist[a] + 1 ) {
                    dist[b] = dist[a] + 1;
                    q.add(b);
                }
            }
        }

        return dist[N-1];
    }

    static class Edge {
        int a, b;

        public Edge(int a, int b) {
            this.a = a;
            this.b = b;
        }
    }


    static int[][] adjD(int n, List<Edge> es) {
        int[][] adj = new int[n][];
        int[] cnt = new int[n];

        for (Edge e : es) {
            cnt[e.a]++;
        }
        for (int i = 0; i < n; i++) {
            adj[i] = new int[cnt[i]];
        }
        for (Edge e : es) {
            adj[e.a][--cnt[e.a]] = e.b;
        }
        return adj;
    }

    @SuppressWarnings("unused")
    static class FastScanner {
        private BufferedReader reader;
        private StringTokenizer tokenizer;

        FastScanner(InputStream in) {
            reader = new BufferedReader(new InputStreamReader(in));
            tokenizer = null;
        }

        String next() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        String nextLine() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    return reader.readLine();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken("\n");
        }

        long nextLong() {
            return Long.parseLong(next());
        }

        int nextInt() {
            return Integer.parseInt(next());
        }

        int[] nextIntArray(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++) a[i] = nextInt();
            return a;
        }

        int[] nextIntArray(int n, int delta) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++) a[i] = nextInt() + delta;
            return a;
        }

        long[] nextLongArray(int n) {
            long[] a = new long[n];
            for (int i = 0; i < n; i++) a[i] = nextLong();
            return a;
        }
    }

    static void writeLines(int[] as) {
        PrintWriter pw = new PrintWriter(System.out);
        for (int a : as) pw.println(a);
        pw.flush();
    }

    static void writeLines(long[] as) {
        PrintWriter pw = new PrintWriter(System.out);
        for (long a : as) pw.println(a);
        pw.flush();
    }

    static void writeSingleLine(int[] as) {
        PrintWriter pw = new PrintWriter(System.out);
        for (int i = 0; i < as.length; i++) {
            if (i != 0) pw.print(" ");
            pw.print(as[i]);
        }
        pw.println();
        pw.flush();
    }

    static int max(int... as) {
        int max = Integer.MIN_VALUE;
        for (int a : as) max = Math.max(a, max);
        return max;
    }

    static int min(int... as) {
        int min = Integer.MAX_VALUE;
        for (int a : as) min = Math.min(a, min);
        return min;
    }

    static void debug(Object... args) {
        StringJoiner j = new StringJoiner(" ");
        for (Object arg : args) {
            if (arg == null) j.add("null");
            else if (arg instanceof int[]) j.add(Arrays.toString((int[]) arg));
            else if (arg instanceof long[]) j.add(Arrays.toString((long[]) arg));
            else if (arg instanceof double[]) j.add(Arrays.toString((double[]) arg));
            else if (arg instanceof Object[]) j.add(Arrays.toString((Object[]) arg));
            else j.add(arg.toString());
        }
        System.err.println(j.toString());
    }

    static void printSingleLine(int[] array) {
        PrintWriter pw = new PrintWriter(System.out);
        for (int i = 0; i < array.length; i++) {
            if (i != 0) pw.print(" ");
            pw.print(array[i]);
        }
        pw.println();
        pw.flush();
    }

    static int lowerBound(int[] array, int value) {
        int lo = 0, hi = array.length, mid;
        while (lo < hi) {
            mid = (hi + lo) / 2;
            if (array[mid] < value) lo = mid + 1;
            else hi = mid;
        }
        return lo;
    }

    static int upperBound(int[] array, int value) {
        int lo = 0, hi = array.length, mid;
        while (lo < hi) {
            mid = (hi + lo) / 2;
            if (array[mid] <= value) lo = mid + 1;
            else hi = mid;
        }
        return lo;
    }
}



Measured memory_bytes: 66956