// >>> TEMPLATES
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using i32 = int32_t;
using i64 = int64_t;
using u32 = uint32_t;
using u64 = uint64_t;
#define int ll
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rep1(i, n) for (int i = 1; i <= (int)(n); i++)
#define repR(i, n) for (int i = (int)(n)-1; i >= 0; i--)
#define rep1R(i, n) for (int i = (int)(n); i >= 1; i--)
#define loop(i, a, B) for (int i = a; i B; i++)
#define loopR(i, a, B) for (int i = a; i B; i--)
#define all(x) begin(x), end(x)
#define allR(x) rbegin(x), rend(x)
#define pb push_back
#define eb emplace_back
#define fst first
#define snd second
template <class Int> auto constexpr inf_ = numeric_limits<Int>::max()/2-1;
auto constexpr INF32 = inf_<int32_t>;
auto constexpr INF64 = inf_<int64_t>;
auto constexpr INF   = inf_<int>;
#ifdef LOCAL
#include "debug.hpp"
#define if_LOCAL(x, y) (x)
#else
#define dump(...) (void)(0)
#define say(x) (void)(0)
#define debug if (0)
#define if_LOCAL(x, y) (y)
#endif
template <class T, class Comp> struct pque : priority_queue<T, vector<T>, Comp> { vector<T> &data() { return this->c; } void clear() { this->c.clear(); } };
template <class T> using pque_max = pque<T, less<T>>;
template <class T> using pque_min = pque<T, greater<T>>;
template <class T, class = typename T::iterator, enable_if_t<!is_same<T, string>::value, int> = 0>
ostream& operator<<(ostream& os, T const& a) { bool f = true; for (auto const& x : a) os << (f ? "" : " ") << x, f = false; return os; }
template <class T, size_t N, enable_if_t<!is_same<T, char>::value, int> = 0>
ostream& operator<<(ostream& os, const T (&a)[N]) { bool f = true; for (auto const& x : a) os << (f ? "" : " ") << x, f = false; return os; }
template <class T, class = decltype(begin(declval<T&>())), class = typename enable_if<!is_same<T, string>::value>::type>
istream& operator>>(istream& is, T &a) { for (auto& x : a) is >> x; return is; }
template <class T, class S> ostream& operator<<(ostream& os, pair<T, S> const& p) { return os << p.first << " " << p.second; }
template <class T, class S> istream& operator>>(istream& is, pair<T, S>& p) { return is >> p.first >> p.second; }
struct IOSetup { IOSetup() { cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(15); } } iosetup;
template <class F> struct FixPoint : private F {
    constexpr FixPoint(F&& f) : F(forward<F>(f)) {}
    template <class... T> constexpr auto operator()(T&&... x) const { return F::operator()(*this, forward<T>(x)...); }
};
struct MakeFixPoint { template <class F> constexpr auto operator|(F&& f) const { return FixPoint<F>(forward<F>(f)); } };
#define MFP MakeFixPoint()|
#define def(name, ...) auto name = MFP [&](auto &&name, __VA_ARGS__)
template <class T, size_t d> struct vec_impl {
    using type = vector<typename vec_impl<T, d-1>::type>;
    template <class... U> static type make_v(size_t n, U&&... x) { return type(n, vec_impl<T, d-1>::make_v(forward<U>(x)...)); }
};
template <class T> struct vec_impl<T, 0> { using type = T; static type make_v(T const& x = {}) { return x; } };
template <class T, size_t d = 1> using vec = typename vec_impl<T, d>::type;
template <class T, size_t d = 1, class... Args> auto make_v(Args&&... args) { return vec_impl<T, d>::make_v(forward<Args>(args)...); }
template <class T> void quit(T const& x) { cout << x << endl; exit(0); }
template <class T, class U> constexpr bool chmin(T& x, U const& y) { if (x > (T)y) { x = (T)y; return true; } return false; }
template <class T, class U> constexpr bool chmax(T& x, U const& y) { if (x < (T)y) { x = (T)y; return true; } return false; }
template <class It> constexpr auto sumof(It b, It e) { return accumulate(b, e, typename iterator_traits<It>::value_type{}); }
template <class T> int sz(T const& x) { return x.size(); }
template <class C, class T> int lbd(C const& v, T const& x) { return lower_bound(begin(v), end(v), x)-begin(v); }
template <class C, class T> int ubd(C const& v, T const& x) { return upper_bound(begin(v), end(v), x)-begin(v); }
constexpr ll mod(ll x, ll m) { assert(m > 0); return (x %= m) < 0 ? x+m : x; }
constexpr ll div_floor(ll x, ll y) { assert(y != 0); return x/y - ((x^y) < 0 and x%y); }
constexpr ll div_ceil(ll x, ll y) { assert(y != 0); return x/y + ((x^y) > 0 and x%y); }
constexpr int dx[] = { 1, 0, -1, 0, 1, -1, -1, 1 };
constexpr int dy[] = { 0, 1, 0, -1, 1, 1, -1, -1 };
constexpr int popcnt(ll x) { return __builtin_popcountll(x); }
mt19937_64 seed_{random_device{}()};
template <class Int> Int rand(Int a, Int b) { return uniform_int_distribution<Int>(a, b)(seed_); }
i64 irand(i64 a, i64 b) { return rand<i64>(a, b); } // [a, b]
u64 urand(u64 a, u64 b) { return rand<u64>(a, b); } //
template <class It> void shuffle(It l, It r) { shuffle(l, r, seed_); }
template <class V> V &operator--(V &v) { for (auto &x : v) --x; return v; }
template <class V> V &operator++(V &v) { for (auto &x : v) ++x; return v; }
bool next_product(vector<int> &v, int m) {
    repR (i, v.size()) if (++v[i] < m) return true; else v[i] = 0;
    return false;
}
bool next_product(vector<int> &v, vector<int> const& s) {
    repR (i, v.size()) if (++v[i] < s[i]) return true; else v[i] = 0;
    return false;
}
template <class vec> int sort_unique(vec &v) {
    sort(begin(v), end(v));
    v.erase(unique(begin(v), end(v)), end(v));
    return v.size();
}
template <class V> auto prefix_sum(V const& a) {
    vector<typename V::value_type> s;
    s.reserve(a.size() + 1);
    s.push_back(0);
    for (auto const& x : a) s.emplace_back(s.back() + x);
    return s;
}
template <class V> auto suffix_sum(V const& a) {
    vector<typename V::value_type> s(a.size() + 1);
    int pos = a.size();
    for (auto it = a.rbegin(); it != a.rend(); ++it, --pos) {
        s[pos-1] = *it + s[pos];
    }
    return s;
}
// <<<
// >>> segment tree

template <class Handler> struct Segtree : Handler {
    using Value = typename Handler::Value;
    using Handler::unit_value;  // () -> Value
    using Handler::merge; // (Value, Value) -> Value

    vector<Value> v;
    int n;

    Segtree() {}
    template <class... T> Segtree(T&&... x) { init(forward<T>(x)...); }

    template <class F, class = decltype(declval<F>()(0))>
    void init(int n, F gen)  {
        assert(n >= 0);
        this->n = n;
        v.resize(2*n, unit_value());
        for (int i = 0; i < n; i++) v[n+i] = gen(i);
        for (int i = n-1; i >= 1; i--) v[i] = merge(v[i<<1], v[i<<1|1]);
    }
    void init(int n) { init(n, [&](int) { return unit_value(); }); }
    void init(int n, Value const& x) { init(n, [&](int) { return x; }); }
    void init(vector<Value> const& v) { init(v.size(), [&](int i) { return v[i]; }); }
    int size() const { return n; }

    void set(int i, Value const& x) {
        assert(0 <= i); assert(i < size());
        i += n; v[i] = x;
        while (i >>= 1) v[i] = merge(v[i<<1], v[i<<1|1]);
    }
    Value operator[](int i) const { return get(i); }
    Value get(int i) const {
        assert(0 <= i); assert(i < size());
        return v[n + i];
    }
    // [l, r)
    Value get(int l, int r) const {
        assert(0 <= l); assert(l <= r); assert(r <= size());
        Value x = unit_value(), y = unit_value();
        for (l += n, r += n; l < r; l >>= 1, r >>= 1) {
            if (l&1) x = merge(x, v[l++]);
            if (r&1) y = merge(v[--r], y);
        }
        return merge(x, y);
    }
    Value get_all() const { return get(0, size()); }
    template <class F> int max_right(int l, F f) {
        assert(0 <= l); assert(l <= size());
        assert(f(unit_value()));
        l += n;
        const int r = size() << 1;
        Value x = unit_value();
        while (true) {
            if (l == r) return size();
            int k = __builtin_ctz(l | 1 << __lg(r - l));
            auto y = merge(x, v[l >> k]);
            if (not f(y)) { l >>= k; break; }
            x = y, l += 1 << k;
        }
        while (l < size()) {
            auto y = merge(x, v[l <<= 1]);
            if (f(y)) x = y, l++;
        }
        return l - size();
    }
    template <class F> int min_left(int r, F f) {
        assert(0 <= r); assert(r <= size());
        assert(f(unit_value()));
        r += n;
        const int l = size();
        Value x = unit_value();
        while (true) {
            if (l == r) return 0;
            int k = __builtin_ctz(r | 1 << __lg(r - l));
            auto y = merge(v[(r >> k) - 1], x);
            if (not f(y)) { r >>= k; --r; break; }
            x = y, r -= 1 << k;
        }
        while (r < size()) {
            r = r << 1 | 1;
            auto y = merge(v[r], x);
            if (f(y)) x = y, r--;
        }
        return r + 1 - size();
    }
    vector<Value> dat() const {
        vector<Value> ret(size());
        for (int i = 0; i < size(); i++) ret[i] = get(i);
        return ret;
    }
};

// <<<

struct Min {
    using Value = int;
    constexpr static Value unit_value() { return INF; }
    constexpr static Value merge(Value const& x, Value const& y) {
        return min(x, y);
    }
};

int32_t main() {
    int n; cin >> n;
    vector<int> r(n-1); cin >> r;

    Segtree<Min> dp(n);
    dp.set(n-1, 0);
    repR (i, n-1) dp.set(i, 1 + dp.get(i+1, r[i]));
    cout << dp[0] << '\n';


}