#include <bits/stdc++.h>

using namespace std;

int main(){

    int x;

    while(x!=0){

        scanf("%d", &x);
        for(int i=1;i<=x;i++){

            int k;
            scanf("%d", &k);
            int m=1;
            stack<int>pilha;
            if(k==m){m++;}
            else if(k!=m){
                pilha.push(k);
                m++;
            }
            else if(pilha.top()==m){
                pilha.pop();
                m++;
            }
            else if(i==m){
                if(pilha.size()==0){printf("yes\n");}
                else if(pilha.size()!=0){printf("no\n");}
            }
        }
    }
    return 0;
}