文件目录

/*#include <iostream>
#include <stack>
using namespace std;
int main(){
    int n,a[1050]={},b[1050]={};
    cin>>n;
    for(int i=1;i<=n;i++) a[i]=i;
    //for(int i=1;i<=n;i++) cin>>a[i];
    for(int i=1;i<=n;i++) cin>>b[i];
    stack<int> c;
    int j=1;//a的当前车头
    for(int i=1;i<=n;i++){
        int x=b[i];//以x为目标，查看c中是否有x车
        if(c.empty()) c.push(a[j++]);
        if(c.top()==x) c.pop();
        else{
            while(j<=n&&a[j]!=x) c.push(a[j++]);
            if(a[j]==x) j++;
            else { cout<<"NO";return 0; }
        }
    }
    cout<<"YES";
    return 0;
}*/

#include <iostream>
using namespace std;
int main()
{
    int n, a[1050] = {}, b[1050] = {};
    cin >> n;
    for (int i = 1; i <= n; i++)
        a[i] = i;
    // for(int i=1;i<=n;i++) cin>>a[i];
    for (int i = 1; i <= n; i++)
        cin >> b[i];
    int c[1050] = {}, t = 0;
    int j = 1; // a的当前车头
    for (int i = 1; i <= n; i++)
    {
        int x = b[i]; // 以x为目标，查看c中是否有x车
        if (t == 0)
            c[t++] = a[j++];
        if (c[t - 1] == x)
            t--;
        else
        {
            while (j <= n && a[j] != x)
                c[t++] = a[j++];
            if (a[j] == x)
                j++;
            else
            {
                cout << "NO";
                return 0;
            }
        }
    }
    cout << "YES";
    return 0;
}