#include <bits/stdc++.h> #define ll long long #define ull unsigned long long #define fi first #define se second using namespace std; ll n; const ll N=1e5+5; ll a[N]; void solve() { stack<ll> sta; set<ll> sett; ll k=1; for(int i=0;i<n;i++) { if(a[i]==k) { k++; while(1) { if(sett.count(k)!=0) { if(sta.top()!=k) { cout<<"no"; return; } else { k++; sta.pop(); } } else break; } } else { sta.push(a[i]); sett.insert(a[i]); } } cout<<"yes"; } int main() { ios::sync_with_stdio(0); cin.tie(0);cout.tie(0); while(1) { cin>>n; if(n==0) break; for(int i=0;i<n;i++) cin>>a[i]; solve(); cout<<endl; } return 0; }