void main(){
  import std.stdio, std.string, std.conv, std.algorithm;

  int n; rd(n);
  auto d=new int[](n);
  foreach(i; 0..n) rd(d[i]);

  int r=0;
  foreach(int i, int e; d){
    if(r<i*10){writeln("no"); return;}
    if(r<i*10+e) r=i*10+e;
  }

  reverse(d);
  r=0;
  foreach(int i, int e; d){
    if(r<i*10){writeln("no"); return;}
    if(r<i*10+e) r=i*10+e;
  }

  writeln("yes");
}

void chmax(T)(ref T x, T y){
  if(x<y) x=y;
}
void rd(T...)(ref T x){
  import std.stdio, std.string, std.conv;
  auto l=readln.split;
  foreach(i, ref e; x){
    e=l[i].to!(typeof(e));
  }
}