#include <bits/stdc++.h>
using namespace std;

#define viktor vector
#define forn(i, s, e) for(ll i=s;i<e;++i)
#define x first
#define y second
#define pii pair <int, int>
#define pll pair <ll, ll>

typedef long long ll;

template <typename T>
ostream&operator << (ostream&out, viktor <T>&v){
    forn(i,0,v.size()) cout << v[i] << " ";
}

template <typename T>
istream&operator >> (istream&in, viktor <T>&v){
    forn(i,0,v.size()) cin >>  v[i];
}

const ll INF=1000000000+1;

int main(){
    int a;
    ll mi=INF, ma=-INF;
    cin >> a;
    viktor <ll> v(a);
    ll t;
    string s;
    for (int i=0;i<a;++i){
        t=0;
        cin >> s;
        if (s.size()==1 && (s[0]<='0' || s[0]>='9')){
            v[i]=INF;
            continue;
        }
        else {
            for (int j=s.size()-1;j>-1;--j){
                t=t*10+int(s[j]-'0');
            }
        }
        v[i]=t;
    }
    for (int i=0;i<a-1;++i){
        if (v[i]==INF && v[i+1]==INF){
            cout << "none";
            return 0;
        }
        if (v[i]!=INF && v[i+1]!=INF){
            if ((i+1)%2==1){
                if (v[i]>=v[i+1]){
                    cout << "none";
                    return 0;
                }
            }
                else {
                    if (v[i]<=v[i+1]){
                        cout << "none";
                        return 0;
                    }
                }

        }
    }
    for (int i=1;i<a-1;++i){
        if (v[i]==INF){
            if ((i+1)%2==0){
                if (v[i-1]!=INF && v[i-1]>ma) ma=v[i-1];
                if (v[i+1]!=INF && v[i+1]>ma) ma=v[i+1];
            }
            else {
                if (v[i-1]!=INF && v[i-1]<mi) mi=v[i-1];
                if (v[i+1]!=INF && v[i+1]<mi) mi=v[i+1];
            }
        }
    }
    if (v[0]==INF){
        if (v[1]!=INF && v[1]<mi) mi=v[1];
    }
    if (v[a-1]==INF){
        if (a%2==0){
            if (v[a-2]!=INF && v[a-2]>ma) ma=v[a-2];
        }
        else{
            if (v[a-2]!=INF && v[a-2]<mi) mi=v[a-2];
        }
    }
    if (mi-ma==2){
        cout << mi-1;
    }
    else if(mi-ma<2){
        cout << "none";
    }
    else{
        cout << "ambiguous";
    }
}