#include <bits/stdc++.h>

#define rep(i,n) for(long long int (i)=0;(i)<(int)(n);(i)++)
#define rrep(i,a,b) for(long long int i=(a);i<(b);i++)
#define rrrep(i,a,b) for(long long int i=(a);i>=(b);i--)
#define all(v) (v).begin(), (v).end()
#define pb(q) push_back(q)
#define Abs(a,b) max(a,b)-min(a,b)
#define YES(condition) if(condition){cout << "YES" << endl;}else{cout << "NO" << endl;}
#define Yes(condition) if(condition){cout << "Yes" << endl;}else{cout << "No" << endl;}
#define Cout(x) cout<<(x)<<endl
#define POSSIBLE(condition) if(condition){cout << "POSSIBLE" << endl;}else{cout << "IMPOSSIBLE" << endl;}
#define Possible(condition) if(condition){cout << "Possible" << endl;}else{cout << "Impossible" << endl;}
#define possible(condition) if(condition){cout << "possible" << endl;}else{cout << "impossible" << endl;}
#define Size(n) (n).size()

typedef long long ll;


using namespace std;

const int INF = 1e9,MOD = 1e9 + 7,ohara = 1e6;
const ll LINF = 1e18;


long long int n,cnt=0,ans=0,a,b,c,d[ohara],cmp,cmpp,m,h,w,x,y,sum=0,pos,ca=0;
int dy[]={1,0,-1,0};
int dx[]={0,1,0,-1};
string alph("abcdefghijklmnopqrstuvwxyz"),s;
bool fl;
struct edge{int to,cost;};

//-------------------------↓↓↓↓↓↓------------------------

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

      
     cin >> n;
     rep(i,n){
       cin >> d[i];
       d[i] /= 10;
     }
     ca = d[0];
     rrep(i,1,n){
       if(ca < i){
         Cout("no");
         return 0;
       }
       ca = max(ca,i + d[i]);
       if(ca == n - 1)break;
     }
     reverse(d,d + n);
     ca = d[0];
     rrep(i,1,n){
       if(ca < i){
         Cout("no");
         return 0;
       }
       ca = max(ca,i + d[i]);
       if(ca == n - 1)break;
     }
     Cout("yes");


       
return 0;
}

