0362:

#include
#include
#include
using namespace std;
 
bool solve(vector v){
  int maxp = 0;
  for ( int i = 0; i < v.size(); i++ ){
    if ( i*10 <= maxp ){
      maxp = max(maxp, v[i] + i*10);
    } else return false;
  }
  return 10*(v.size()-1) <= maxp;
}
 
main(){
  int N; cin >> N;
  vector v, u;
  for ( int i = 0; i < N; i++ ){
    int x; cin >> x; v.push_back(x);
  }
  u = v;
  reverse(u.begin(), u.end());
 
  cout << (solve(v)&&solve(u)?"yes":"no") << endl;
 
  return 0;
}