#include <bits/stdc++.h>
using namespace std;

struct
{
    int data, l, r;
} tree[25];

int p = -1;
vector<int> v;

int build(int root, int x)
{
    if (root == -1)
    {
        tree[++p].data = x;
        tree[p].l = tree[p].r = -1;
        return p;
    }

    if (x > tree[root].data) tree[root].l = build(tree[root].l, x);
    else tree[root].r = build(tree[root].r, x);

    return root;
}

void bfs(int x)
{
    cout << tree[x].data;
    queue<int> que;
    que.push(x);

    while (que.size())
    {
        int t = que.front();
        que.pop();

        v.push_back(tree[t].l);
        v.push_back(tree[t].r);

        if (tree[t].l != -1)
        {
            cout << ' ' << tree[tree[t].l].data;
            que.push(tree[t].l);
        }

        if (tree[t].r != -1)
        {
            cout << ' ' << tree[tree[t].r].data;
            que.push(tree[t].r);
        }
    }
}

int main()
{
    int n;
    cin >> n;
    int root = -1;
    while (n--)
    {
        int x;
        cin >> x;
        root = build(root, x);
    }

    bfs(root);

    bool f = 1;
    for (int i = 1; i < v.size(); i++)
    {
        if (v[i] != -1 && v[i - 1] == -1)
        {
            f = 0;
            break;
        }
    }

    if (f) puts("\nYES");
    else puts("\nNO");

    return 0;
}