#include <iostream>
#include <iomanip>
#include <string>
#include <algorithm>
#include <cmath>
#include <vector>
#include <queue>
#include <map>
#include <set>
#include <stack>
#include <unordered_map>
#include <unordered_set>
using namespace std;

#define ll long long
#define nl "\n"
#define cy cout << "YES\n"
#define cn cout << "NO\n"
#define sz(s) s.size()
#define all(v) v.begin(), v.end()
#define cin(vec) for (int i = 0; i < n && cin >> vec[i]; i++)
#define cout(vec) for (int i = 0; i < n && cout << vec[i] << " "; i++)

void sherry()
{
    ios_base::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
#ifndef ONLINE_JUDGE
    freopen("input.txt", "r", stdin), freopen("output.txt", "w", stdout);
#endif
}
void solve()
{
    int n;
    cin >> n;
    int arr[n + 5]{};
    stack<int> st;
    for (int i = 0; i < n; i++)
    {
        int num;
        cin >> num;
        for (int j = 1; j <= num; j++)
        {
            if (arr[j] == 0)
            {
                st.push(j);
                arr[j] = 1;
            }
        }
        if (st.top() == num)
        {
            st.pop();
        }
        else
        {
            cn;
            return;
        }
    }
    cy;
}
/*

 */
int main()
{
    sherry();
    int t = 1;
    // cin >> t;
    while (t--)
    {
        solve();
    }
    return 0;
}