#include<bits/stdc++.h>
using namespace std;

#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define ALL(v) v.begin(),v.end()
typedef long long ll;
template <class T> using V=vector<T>;
template <class T> using VV=V<V<T>>;
 
int main(){
  ios::sync_with_stdio(false);
  std::cin.tie(nullptr);
  
  int n;
  cin>>n;
  V<int> A(n);
  rep(i,n) cin>>A[i];
  
  bool b=true;
  deque<int> deq;
  rep(i,n) deq.push_back(A[i]);
  int now=1;
  while(deq.size()){
    if(deq.front()<=now){
      deq.pop_front();
      now++;
    } 
    else if(deq.back()<=now){
      deq.pop_back();
      now++;
    }
    else{
      b=false;
      break;
    }
  }
  if(b) cout<<"Yes"<<endl;
  else cout<<"No"<<endl;
    
  return 0;
}