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#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();
    }
}