#include <bits/stdc++.h>
using namespace std;
#define rep(i,l,r) for(int i=(int)l;i<(int)r;i++)

int main(){
  //subtask1
  int n;cin>>n;
  vector<int> h(n);
  rep(i,0,n)cin>>h[i];
  cout<<(h[0]>h[1]&&h[1]<h[2]&&h[2]>h[3]&&h[3]<h[4]?"Yes":"No");
}