#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