#include<bits/stdc++.h>
using namespace std;
int main()
{
  int n;
  cin>>n;
  int a[n];
  for(int i=0;i<n;i++)
    cin>>a[i];
  for(int i=n-1;i>0;i--)
  {
      if(a[i]<a[i-1]-1)
        return cout<<"No",0;
      else
        if(a[i]==a[i-1]-1)
          a[i-1]--;
  }
  return cout<<"Yes",0;
}