#include<cstdio>

 int n,a[];

 int main(){

     scanf("%d",&n);

     for(int i=;i<=n;++i)scanf("%d",a+i);

     int L=,R=n;

     while(L<n&&a[L]<a[L+])++L;

     while(R>&&a[R]<a[R-])--R;

     for(int i=L+;i<=R;++i)if(a[L]!=a[i])return puts("NO"),;

     return puts("YES"),;

 }

 #include <iostream>

 using namespace std;

 int N;

 int V[];

 int main()

 {

     cin>>N;

     for(int i=;i<=N;i++)cin>>V[i];

     int i=;

     while(i<N&&V[i]<V[i+])i++;

     while(i<N&&V[i]==V[i+])i++;

     while(i<N&&V[i]>V[i+])i++;

     if(i<N)cout<<"NO";

     else cout<<"YES";

     return ;

 }

 #include<iostream>

 #include<cstdio>

 using namespace std;

 int n;

 int a[];

 int main()

 {

     scanf("%d",&n);

     for(int i=;i<=n;i++)scanf("%d",a+i);

     int i=;

     while(i+<=n && a[i+]>a[i])i++;

     while(i+<=n && a[i+]==a[i])i++;

     while(i+<=n && a[i+]<a[i])i++;

     if(i<n)printf("NO");else printf("YES");

     return ;

 } 

 #include<bits/stdc++.h>

 using namespace std;

 int main()

 {

     int n;

     cin>>n;

     int arr[n];

     for(int i=;i<n;i++)

         cin>>arr[i];

     int i=;

     while(arr[i+]>arr[i] && i+<n)

         i++;

     while(arr[i]==arr[i+] && i+<n)

         i++;

     while(arr[i]>arr[i+] && i+<n)

         i++;

     if(i==n-)

         cout<<"YES";

     else cout<<"NO";

 }

 #include <bits/stdc++.h>

 using namespace std;

 int a[];

 int n;

 void sol(string s) {

     cout << s;

     exit();

 }

 int main() {

 #ifndef ONLINE_JUDGE

     freopen("CF.in", "r", stdin);

 #endif

     cin >> n;

     for (int i = ; i <= n; ++i)cin >> a[i];

     int i=;

     while(i+<=n&&a[i]<a[i+])++i;

     while(i+<=n&&a[i]==a[i+])++i;

     while(i+<=n)

     {

         if(a[i]<=a[i+])sol("NO");

         ++i;

     }sol("YES");

 }