/*   @JUDGE_ID:   1705PZ   514   C */
#include <stdio.h>
#include <stdlib.h>

int main()
{
	int i,j,n,temp,ans;
	int *table;
	while(1)
	{
		scanf("%d",&n);
		if(n == 0)
			break;
		table = (int *)malloc(sizeof(int) * n);
		while(1)
		{
			ans = 1;
			scanf("%d",table);
			if(*table == 0)
			{
				printf("\n");
				break;
			}
			for(i = 1;i < n;i++)
				scanf("%d",table + i);
			for(i = 0;i < n;i++)
			{
				temp = *(table + i);
				for(j = i + 1;j < n;j++)
					if(*(table + j) < *(table + i))
					{
						if(*(table + j) > temp)
							ans = 0;
						temp = *(table + j);
					}
			}

			if(ans == 0)
				printf("NO\n");
			else
				printf("YES\n");
		}
		free(table);
	}
	return 0;
}
@END_OF_SOURCE_CODE