#include "bits/stdc++.h"
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
const int INF = 1e9;
const ll LINF = 1e18;
template<class S,class T> ostream& operator << (ostream& out,const pair<S,T>& o){ out << "(" << o.first << "," << o.second << ")"; return out; }
template<class T> ostream& operator << (ostream& out,const vector<T>& V){ for(int i = 0; i < V.size(); i++){ out << V[i]; if(i!=V.size()-1) out << " ";} return out; }
template<class T> ostream& operator << (ostream& out,const vector<vector<T> >& Mat){ for(int i = 0; i < Mat.size(); i++) { if(i != 0) out << endl; out << Mat[i];} return out; }
template<class S,class T> ostream& operator << (ostream& out,const map<S,T>& mp){ out << "{ "; for(auto it = mp.begin(); it != mp.end(); it++){ out << it->first << ":" << it->second; if(mp.size()-1 != distance(mp.begin(),it)) out << ", "; } out << " }"; return out; }
template<typename T>vector<T> make_v(size_t a){return vector<T>(a);}
template<typename T,typename... Ts>auto make_v(size_t a,Ts... ts){return vector<decltype(make_v<T>(ts...))>(a,make_v<T>(ts...));}
template<typename T,typename V> typename enable_if<is_class<T>::value==0>::type fill_v(T &t,const V &v){t=v;}
template<typename T,typename V> typename enable_if<is_class<T>::value!=0>::type fill_v(T &t,const V &v){for(auto &e:t) fill_v(e,v);}
/*
 <url:>
 問題文============================================================
 =================================================================
 解説=============================================================
 ================================================================
 */

template<class Type>
Type solve(Type res = Type()){
    return res;
}
int main(void) {
    cin.tie(0); ios_base::sync_with_stdio(false);
    // solve(0);
    // cout << fixed << setprecision(15) << solve<ll>() << endl;
    int N;
    while(cin >> N,N){
        vector<int> a(N);
        vector<char> x(N);
        for(int i = 0; i < N;i++){
            string s; cin >> s;
            if(s == "x"){
                x[i] = true;
                continue;
            }
            a[i] = atoi(s.c_str());
        }
        bool ng = false;
        for(int i = 1; i < N;i++){ // x x
            if(x[i] && x[i-1]) ng = true;
            if(!x[i] && !x[i-1]){
                if(i&1){
                    if(a[i] <= a[i-1]) ng = true;
                }else{
                    if(a[i] >= a[i-1]) ng = true;
                }
            }
        }
        if(ng){
            cout << "none" << endl;
            continue;
        }
        int l = -2*INF,r = 2*INF;
        for(int i = 0; i < N;i++){
            if(!x[i]) continue;
            if(i!=0){
                if(i&1){
                    l = max(l,a[i-1]+1);
                }else{
                    r = min(r,a[i-1]-1);
                }
            }
            if(i!=N-1){
                if(i&1){
                    l = max(l,a[i+1]+1);
                }else{
                    r = min(r,a[i+1]-1);
                }
            }
        }
        if(l==r){
            cout << l << endl;
        }else if(l < r){
            cout << "ambiguous" << endl;
        }else{
            cout << "none" << endl;
        }
    }
    return 0;
}



Measured memory_bytes: 3188