#include <iostream>
#include <cstdio>
 
using namespace std;
 
int main()
{
	int n;
	cin>>n;
	while(n!=0)
	{
		int a[1100]={0};
		int i = 0;
		while(i < n)
			cin>>a[i++];
		int b[1100]={0};
		int j = -1;
		i = 0;
		int x = 1;
		int flag = 0;
		int n1 = 0;
		while(i<n)
		{
			flag = 0;
			if(j >= 0)
			{
				if(b[j] == x)
				{
					b[j] = 0;
					j--;
					x++;
					flag = 1;
				}
			}
			if(flag == 0)
			{
				if(a[i] == x)
				{
					i++;
					x++;	
				}
				else
				{
					j++;
					n+=1;
					n1++;
					b[j] = a[i++];
					if(b[j] == 0)
						goto endwhile;
				}
			}
		}
		endwhile:
		if(x+n1 == n+1)
			cout<<"yes"<<endl;
		else
			cout<<"no"<<endl;
		cin>>n;
	}
	return 0;
}

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NQo0IDEgNSAzIDIKNQozIDEgMiA1IDQKNQo1IDMgMiAxIDQKMTAKMSAyIDEwIDUgNCAzIDcgNiA4IDkKMTAKMSAyIDEwIDUgNCAzIDkgOCA3IDYKNQozIDUgMiA0IDEKNQoxIDIgNCAzIDUKNAo0IDIgMyAxIAow

5
4 1 5 3 2
5
3 1 2 5 4
5
5 3 2 1 4
10
1 2 10 5 4 3 7 6 8 9
10
1 2 10 5 4 3 9 8 7 6
5
3 5 2 4 1
5
1 2 4 3 5
4
4 2 3 1 
0