//#pragma GCC optimize("Ofast")
#include<bits/stdc++.h>
using namespace::std;
//struct __INIT{__INIT(){cin.tie(0);ios::sync_with_stdio(false);cout<<fixed<<setprecision(15);}} __init;
__attribute__((constructor))
void init(){
	cin.tie(0);
	ios::sync_with_stdio(false);
	cout<<fixed<<setprecision(15);
}
// random_device rd;
// mt19937 mt(rd());
// #include <boost/numeric/interval.hpp>
// #include <boost/numeric/interval/io.hpp>
// #include <boost/intrusive/rbtree.hpp>
// #include <boost/dynamic_bitset.hpp>
// #include <boost/geometry.hpp>
// #include <boost/geometry/geometries/linestring.hpp>
// #include <boost/geometry/geometries/polygon.hpp>
// #include <boost/geometry/geometries/point_xy.hpp>
// #include <boost/math/tools/minima.hpp>
// using boost::math::tools::brent_find_minima;
// #include <boost/multiprecision/cpp_dec_float.hpp>
// #include <boost/multiprecision/cpp_int.hpp>
// namespace mp = boost::multiprecision;
// typedef mp::number<mp::cpp_dec_float<256>> cdouble;
// typedef mp::cpp_int cint;

#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/priority_queue.hpp>
#include<ext/pb_ds/tag_and_trait.hpp>
using namespace __gnu_pbds;
template<typename T=long long>using pbds=tree<T,null_type,less<T>,rb_tree_tag,tree_order_statistics_node_update>;
template<typename T=long long>using pbds_map=tree<T,T,less<T>,rb_tree_tag,tree_order_statistics_node_update>;
template<typename T=long long>using pqueue =__gnu_pbds::priority_queue<T, less<T>,rc_binomial_heap_tag>;
typedef long long lint;
typedef long long ll;
typedef long double ldouble;
typedef vector<lint> vec;
typedef vector<vector<lint>> mat;
typedef vector<vector<vector<lint>>> mat3;
typedef vector<double> dvec;
typedef vector<vector<double>> dmat;
typedef vector<vector<vector<double>>> dmat3;
typedef vector<string> svec;
typedef vector<vector<string>> smat;
typedef vector<vector<vector<string>>> smat3;
typedef vector<pair<lint,lint>> pvec;
typedef vector<vector<pair<lint,lint>>> pmat;
typedef vector<vector<vector<pair<lint,lint>>>> pmat3;
#define rep(i, n) for(lint i = 0; i < (lint)(n); i++)
#define irep(i) for(lint i = 0;; i++)
#define irep1(i) for(lint i = 1;; i++)
#define irep2(i) for(lint i = 2;; i++)
#define rrep(i, n) for(lint i = (lint)(n-1); i >-1; i--)
#define rrepi(i,a,b) for(lint i = (lint)(b-1); i >a-1; i--)
#define repi(i,a,b) for(lint i=lint(a);i<lint(b);i++)
#define rep2(i,a,b,c) for(lint i=lint(a);i>lint(b);i+=c)
#define all(x) (x).begin(),(x).end()
#define PI 3.141592653589793
#define dist(x1,y1,x2,y2) (pow(pow(x2-x1,2)+pow(y2-y1,2),0.5))
#define output(v) do{bool f=0;for(auto i:v){cout<<(f?" ":"");if(i>INF/2)cout<<"INF";else cout<<i;f=1;}cout<<"\n";}while(0);
#define output2(v) for(auto j:v)output(j);
#define _output(v) do{bool f=0;rep(i,v.size()){cout<<(f?" ":"");if(v[i]>INF/2)cout<<"INF";else cout<<v[i];f=1;}cout<<"\n";}while(0)
#define _output2(v) rep(j,v.size()){_output(v[j]);}
#define input(a,n) lint n;cin>>n;vector<lint>a(n);rep(i,n)cin>>a[i];
#define SUM(v) accumulate(all(v),0LL)
#define INF (1LL<<60)
#define IINF (1<<30)
#define EPS (1e-10)
#define LINF 9223372036854775807
#define MOD 998244353LL
#define endl "\n"
template<typename T=lint>T in(){return *istream_iterator<T>(cin);}
inline lint gcd(lint a,lint b){return b?gcd(b,a%b):a;}
template<typename T=lint>inline T lcm(T a,T b){return a/gcd(a,b)*b;}
template<typename T=lint>inline T add(T a,T b){return a+b;}
template<typename T=lint>inline T minq(T a,T b){return min(a,b);}
inline bool chmin(auto& s,const auto& t){bool res=s>t;s=min(s,t);return res;}
inline bool chmax(auto& s,const auto& t){bool res=s<t;s=max(s,t);return res;}
vector<lint> dx={-1,1,0,0,1,1,-1,-1};
vector<lint> dy={0,0,-1,1,1,-1,1,-1};



// template<typename T,typename E>
// struct RBST{
// 	struct node{
// 		int cnt=1,l=-1,r=-1;
// 		T key;E val;
// 		node(){}
// 		node(T key,E val):key(key),val(val){}
// 	};
// 	vector<node> v;
// 	RBST(){
// 	}
// 	int root=1;
// 	int count(int idx){return idx==-1?0:v[idx].cnt;}
// 	int update(int idx){
// 		if(idx!=-1)v[idx].cnt=1+count(v[idx].l)+count(v[idx].r);
// 		return idx;
// 	}
// 	private:
// 	inline int merge(int l,int r){
//         if(l==-1||r==-1)return l==-1?r:l;
//         if((unsigned long)count(v[l])>rnd()%(unsigned long)(count(v[l])+count(v[r]))){
//             v[l].r=merge(v[l].r,r);
//             return update(l);
//         }else{
//             v[r].l=merge(l,v[r].l);
//             return update(r);
//         }
//     }
// 	inline pair<int,int> split(int t,int k){
//         if(t==-1)return make_pair(-1,-1);
//         if(k<=count(v[t].l)){
//             auto s=split(v[t].l,k);
//             v[t].l=s.second;
//             return make_pair(s.first,update(t));
//         }else{
//             auto s=split(v[t].r,k-count(v[t].l)-1);
//             v[t].r=s.first;
//             return make_pair(update(t),s.second);
//         }
//     }
// 	inline unsigned long rnd() {
//         static unsigned long x=123456789, y=362436069, z=521288629, w=88675123;
//         unsigned long t=(x^(x<<11));
//         x=y; y=z; z=w;
//         return ( w=(w^(w>>19))^(t^(t>>8)) );
//     }
// };

template<typename T=long long,typename E=T>
struct segment{
    private:
    T et;
    E ee;
    lint n;
    lint size;
    struct node{
        T val;
        E lazy;
        node *lch,*rch;
        node(segment &seg):lch(nullptr),rch(nullptr){val=seg.et;lazy=seg.ee;}
    };
    struct interval{
        segment<T,E>* seg;
        lint l,r;
        interval operator +=(T n){seg->update(l,r,n);return *this;}
        interval operator =(T n){seg->update(l,r,n);return *this;}
        operator T(){return seg->get(l,r);}
    };
    struct iterator{
        lint n;
        segment<T,E>* seg;
        iterator(segment* seg,lint n):n(n),seg(seg){}
        auto operator!=(const iterator& rhs){return n!=rhs.n;}
        auto operator++(){n++;}
        auto operator--(){n--;}
        auto operator+=(lint add){n+=add;}
        auto operator-=(lint sub){n-=sub;}
        auto operator*(){return seg->get(n,n+1);}
    };
    node* root;
    public:
    segment(lint size,T et,E ee):et(et),ee(ee),n(1),size(size){
        while(n<size)n<<=1;
        root=new node(*this);
    }
    segment(T et,E ee):et(et),ee(ee),n((1LL<<61)-1),size(1LL<<60){
        root=new node(*this);
    }
    public:
    //0-indexed [a,b)
    T update(lint a,lint b,E x,lint k=0,lint l=0,lint r=-1,node* t=nullptr){
        if(t==nullptr)t=root;
        if(r<0)r=n;
        eval(t,r-l,k);
        //区間外
        if(r<=a||b<=l)return t->val;
        //全部区間内
        if(a<=l&&r<=b){
            t->lazy=g(t->lazy,x);
            return h(t->val,t->lazy,r-l);
        }
        //一部区間内
        if(t->lch==nullptr)t->lch=new node(*this);
        if(t->rch==nullptr)t->rch=new node(*this);
        return t->val=f(update(a,b,x,2*k+1,l,(l+r)/2,t->lch),update(a,b,x,2*k+2,(l+r)/2,r,t->rch));
    }
    //0-indexed [a,b)
    T get(lint a,lint b,lint k=0,lint l=0,lint r=-1,node* t=nullptr){
        if(t==nullptr)t=root;
        if(r<0)r=n;
        eval(t,r-l,k);
        //区間外
        if(r<=a||b<=l)return et;
        //全部区間内
        if(a<=l&&r<=b)return t->val;
        //一部区間内
        if(t->lch==nullptr)t->lch=new node(*this);
        if(t->rch==nullptr)t->rch=new node(*this);
        return f(get(a,b,2*k+1,l,(l+r)/2,t->lch),get(a,b,2*k+2,(l+r)/2,r,t->rch));
    }
    iterator begin(){
        return iterator(this,0);
    }
    iterator end(){
        return iterator(this,size);
    }
    interval operator ()(lint l,lint r){return interval{this,l,r};}
    interval operator ()(lint n){return interval{this,n,n+1};}
    interval operator [](lint n){return interval{this,n,n+1};}
    private:
    inline void eval(node* t,lint len,lint k){
        if(t->lazy==ee) return;
        if(k*2+1<n*2-1){
            if(t->lch==nullptr)t->lch=new node(*this);
            if(t->rch==nullptr)t->rch=new node(*this);
            t->lch->lazy=g(t->lch->lazy,t->lazy);
            t->rch->lazy=g(t->rch->lazy,t->lazy);
        }
        t->val=h(t->val,t->lazy,len);
        t->lazy=ee;
    }
    T f(T a,T b){
        return a+b;
    }
    T h(T a,E b,lint len){
        return update(a,b);
    }
    E g(E a,E b){
        return update(a,b);
    }
    auto update(auto a,auto b){return b==ee?a:b;}
};

int main(){
    lint n;
    cin>>n;
    vec a(n);
    rep(i,n)cin>>a[i];
    segment<lint,lint> dp(n,0,0);
    dp[0]=1;
    rep(i,n){
        if(dp[i]==1){
            dp.update(i+1,i+a[i]/10+1,1);
        }
    }
    if(dp[n-1]==0){
        cout<<"no"<<endl;
        return 0;
    }
    dp=segment<lint,lint>(n,0,0);
    dp[0]=1;
    reverse(all(a));
    rep(i,n){
        if(dp[i]==1){
            dp.update(i+1,i+a[i]/10+1,1);
        }
    }
    if(dp[n-1]==0){
        cout<<"no"<<endl;
        return 0;
    }
    cout<<"yes"<<endl;
}


Measured memory_bytes: 80096