#include "bits/stdc++.h"
// @JASPER'S BOILERPLATE
using namespace std;
using ll = long long;
#define FOR(i, a, b) for(int i = a; i <= b; i++)
#define FORD(i, a, b) for(int i = a; i >= b; i--)
#define REP(i, b) for(int i = 0; i < b; i++)
#define PER(i, b) for(int i = b - 1; i >= 0; i--)
#define fi first
#define se second
#ifdef JASPER2
#include "debug.h"
#else
#define debug(...) 166
#endif
using pii = pair < int, int >;
const int INF = 1e9;
const int MOD = 1e9 + 7;
const int N = 1e2 + 5;
int n;
void run_case() {
cin >> n;
vector <int> a(n), b(n);
for (int i = 0; i < n; ++i) cin >> a[i];
b = a;
sort(b.begin(), b.end());
for (int i = 0; i < n; ++i) {
if (a[i] != b[n - i - 1] && a[i] != b[i]) {
cout << "NO\n";
return;
}
}
cout << "YES\n";
}
signed main() {
cin.tie(0) -> sync_with_stdio(0);
#ifdef JASPER2
freopen("in1", "r", stdin);
#endif
int Test = 1;
//cin >> Test;
for (int test = 1; test <= Test; test++){
run_case();
}
}