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

#define fi first
#define se second
#define repl(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define repr(i,n) for(int i=(int)(n-1);i>=0;i--)
#define rep(i,n) repl(i,0,n)
#define each(itr,v) for(auto itr:v)
#define pb(s) push_back(s)
#define all(x) (x).begin(),(x).end()
#define dbg(x) cout << #x" = " << x << endl
#define print(x) cout << x << endl
#define maxch(x,y) x=max(x,y)
#define minch(x,y) x=min(x,y)
#define uni(x) x.erase(unique(all(x)),x.end())
#define exist(x,y) (find(all(x),y)!=x.end())
#define bcnt(x) bitset<32>(x).count()

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> P;
typedef pair<P, int> PPI;
typedef pair<int, P> PIP;
typedef pair<ll, ll> PL;
typedef pair<P, ll> PPL;
typedef set<int> S;

#define INF INT_MAX/3
#define MAX_N 1000000000


int main(){
    cin.sync_with_stdio(false);
    int n;
    while(cin >> n, n) {
        string a[n];
        rep(i, n) cin >> a[i];
        int maxi = MAX_N + 2, mini = -MAX_N - 2;
        rep(i, n) {
            if (a[i][0] == 'x') {
                if (0 < i) {
                    if (a[i - 1][0] == 'x') {
                        maxi = -MAX_N, mini = MAX_N;
                        break;
                    }
                    if (i % 2) maxch(mini, stoi(a[i - 1]) + 1);
                    else minch(maxi, stoi(a[i - 1]) - 1);
                }
                if (i < n - 1) {
                    if (a[i + 1][0] == 'x') {
                        maxi = -MAX_N, mini = MAX_N;
                        break;
                    }
                    if (i % 2) maxch(mini, stoi(a[i + 1]) + 1);
                    else minch(maxi, stoi(a[i + 1]) - 1);
                }
            } else {
                int p = stoi(a[i]);
                if (0 < i && a[i - 1][0] != 'x') {
                    int q = stoi(a[i - 1]);
                    if ((i % 2 && p <= q) || (!(i % 2) && p >= q)) {
                        maxi = -MAX_N, mini = MAX_N;
                        break;
                    }
                }
                if (i < n - 1 && a[i + 1][0] != 'x') {
                    int q = stoi(a[i + 1]);
                    if ((i % 2 && p <= q) || (!(i % 2) && p >= q)) {
                        maxi = -MAX_N, mini = MAX_N;
                        break;
                    }
                }
            }
        }

        if (maxi < mini) cout << "none" << endl;
        else if (maxi > mini) cout << "ambiguous" << endl;
        else cout << maxi << endl;
    }

    return 0;
}