#include<iostream>
#include<vector>
#include<stack>
using namespace std;

struct Point
{
    int from;
    int vagon;
};

int main()
{
    int n;
    cin >> n;
    vector<int> v(n);
    for(int i = 0; i < n; ++i) cin >> v[i];
    stack<int> way_1;
    stack<int> stop;
    stack<int> way_2;
    vector<pair<int, int> > ans;
    ans[i].second =
    for(int i = n - 1; i >= 0; i--) way_1.push(v[i]);
    int i = 1;
    int x;
    while(way_1.size() > 0)
    {
        while(way_1.top() != i)
        {
            x = way_1.top();
            stop.push(x);
            way_1.pop();
        }
        x = way_1.top();
        way_2.push(x);
        way_1.pop();
        i++;
        while(stop.top() == i)
        {
            x =  stop.top();
            way_2.push(x);
            stop.pop();
            i++;
        }
    }
    if(way_2.size() == n) cout << "YES";
    else cout << "NO";
}