#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(i=0;i<n;i++)
#define rep1(i,n) for (i=1; i<=n ;i++)
#define gi(n) cin >> n
#define pi(n) cout << n
#define pn printf("\n")
typedef long long ll;
#define MAX 111111
ll order[MAX];
 
int main() {
	int i, n, flag, need;
	cin >> n;
	while(n!=0){
		stack <int> lane;
		need = 1;
		bool state = true;
		rep(i,n) gi(order[i]);
		rep(i,n) {
			while (!lane.empty() && lane.top() == need) {
				need++;
				lane.pop();
			}
			if (order[i] == need) {
				need++;
			} 
			else if (!lane.empty() && lane.top() < order[i]) {
				state = false;
				break;
			} 
			else {
				lane.push(order[i]);
			}
		}
		if (state) cout << "yes" << "\n";
		else cout << "no" << "\n";
		gi(n);
	}
	return 0;
}

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

NSAKNCAxIDUgMyAyIAo1IAozIDEgMiA1IDQgCjUgCjUgMyAyIDEgNCAKMTAgCjEgMiAxMCA1IDQgMyA3IDYgOCA5IAoxMCAKMSAyIDEwIDUgNCAzIDkgOCA3IDYgCjUgCjMgNSAyIDQgMSAKNSAKMSAyIDQgMyA1IAo0IAo0IDIgMyAxIAow

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