// #pragma GCC ta g("avx2")
// #pragma GCC optimize("Ofast")
// #pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
using namespace std;
#define DEBUG
#ifdef DEBUG
template <class T, class U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
    os << '(' << p.first << ',' << p.second << ')';
    return os;
}
template <class T> ostream &operator<<(ostream &os, const vector<T> &v) {
    os << '{';
    for(int i = 0; i < (int)v.size(); i++) {
        if(i) { os << ','; }
        os << v[i];
    }
    os << '}';
    return os;
}
void debugg() { cerr << endl; }
template <class T, class... Args>
void debugg(const T &x, const Args &... args) {
    cerr << " " << x;
    debugg(args...);
}
#define debug(...)                                                             \
    cerr << __LINE__ << " [" << #__VA_ARGS__ << "]: ", debugg(__VA_ARGS__)
#define dump(x) cerr << __LINE__ << " " << #x << " = " << (x) << endl
#else
#define debug(...) (void(0))
#define dump(x) (void(0))
#endif
using namespace std;
typedef long long ll;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<char> vc;
typedef vector<string> vs;
typedef vector<bool> vb;
typedef vector<double> vd;
typedef pair<ll,ll> P;
typedef pair<int,int> pii;
typedef vector<P> vpl;
typedef tuple<ll,ll,ll> tapu;
#define rep(i,n) for(int i=0; i<(n); i++)
#define REP(i,a,b) for(int i=(a); i<(b); i++)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
template<typename T1,typename T2> inline bool chmin(T1 &a,T2 b){
	if(a>b){
		a = b; return true;
	}
	else return false;
}
template<typename T1,typename T2> inline bool chmax(T1 &a,T2 b){
	if(a<b){
		a = b; return true;
	}
	else return false;
}
template<typename T> inline void print(T &a){
    int sz = a.size();
    for(auto itr = a.begin(); itr != a.end(); itr++){
		cout << *itr;
        sz--;
        if(sz) cout << " ";
	}
    cout << "\n";
}
template<typename T1,typename T2> inline void print2(T1 a, T2 b){
	cout << a << " " << b << "\n";
}
template<typename T1,typename T2,typename T3> inline void print3(T1 a, T2 b, T3 c){
	cout << a << " " << b << " " << c << "\n";
}
void mark() {cout << "#" << "\n";}
ll pcount(ll x) {return __builtin_popcountll(x);}
//#include <atcoder/maxflow>
//using namespace atcoder;
const int inf = (1<<30)-1;
const ll linf = 1LL<<61;
const int MAX = 20200000;
int dy[8] = {0,1,0,-1,1,-1,-1,1};
int dx[8] = {-1,0,1,0,1,-1,1,-1};
const double pi = acos(-1);
const double eps = 1e-9;
const int mod = 1e9 + 7;
//const int mod = 998244353;

template<typename Monoid>
struct Segtree {
    using F = function<Monoid(Monoid, Monoid)>;
    int sz;
    vector<Monoid> seg;
    const F f;
    const Monoid M;

    Segtree(int n, const F f, const Monoid &M) : f(f), M(M){
        sz = 1;
        while(sz < n) sz <<= 1;
        seg.assign(2*sz, M);
    }

    void set(int k, const Monoid &x) {
        seg[k + sz] = x;
    }

    void build(){
        for(int k=sz-1; k>0; k--){
            seg[k] = f(seg[2*k], seg[2*k+1]);
        }
    }

    void update(int k, const Monoid &x){
        k += sz;
        seg[k] = x;
        while(k >>= 1){
            seg[k] = f(seg[2*k], seg[2*k+1]);
        }
    }

    Monoid query(int a, int b){
        Monoid L = M, R = M;
        for(a += sz, b += sz; a < b; a >>= 1, b >>= 1){
            if(a & 1) L = f(L, seg[a++]);
            if(b & 1) R = f(seg[--b], R);
        }
        return f(L, R);
    }

    Monoid operator[](const int &k) const {
        return seg[k + sz];
    }

    template<typename C>
    int find_subtree(int a, const C &check, Monoid &M0, bool type){
        while(a < sz){
            Monoid nxt = type ? f(seg[2*a+type],M0) : f(M0,seg[2*a+type]);
            if(check(nxt)) a = 2 * a + type;
            else M0 = nxt, a = 2 * a + 1 - type;
        }
        return a - sz;
    }

    template<typename C>
    int find_first(int a, const C &check){
        Monoid L = M;
        if(a <= 0){
            if(check(f(L, seg[1]))) return find_subtree(1,check,L,false);
            return -1;
        }
        int b = sz;
        for(a += sz, b += sz; a < b; a >>= 1, b >>= 1){
            if(a & 1){
                Monoid nxt = f(L, seg[a]);
                if(check(nxt)) return find_subtree(a,check,L,false);
                L = nxt;
                ++a;
            }
        }
        return -1;
    }

    template<typename C>
    int find_last(int b, const C &check){
        Monoid R = M;
        if(b >= sz){
            if(check(f(seg[1], R))) return find_subtree(1,check,R,true);
            return -1;
        }
        int a = sz;
        for(b += sz; a < b; a >>= 1, b >>= 1){
            if(b & 1){
                Monoid nxt = f(seg[--b], R);
                if(check(nxt)) return find_subtree(b,check,R,true);
                R = nxt;
            }
        }
        return -1;
    }
};

int main(){
    int n; cin >> n;
    vl r(n-1); rep(i,n-1) cin >> r[i];
    Segtree<int> seg(n,[](int a, int b){return min(a,b);},inf);
    seg.update(n-1,0);
    for(int i=n-2; i>=0; i--){
        seg.update(i,seg.query(i+1,r[i])+1);
    }
    cout << seg[0] << "\n";
}