#include <cstdio>
#include <iostream>
#include <string>
#include <sstream>
#include <stack>
#include <algorithm>
#include <cmath>
#include <queue>
#include <map>
#include <set>
#include <cstdlib>
#include <bitset>
#include <tuple>
#include <assert.h>
#include <deque>
#include <bitset>
#include <iomanip>
#include <limits>
#include <chrono>
#include <random>
#include <array>
#include <unordered_map>
#include <functional>
#include <complex>
#include <numeric>
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

constexpr long long MAX = 5100000;
constexpr long long INF = 1LL << 60;
constexpr int inf = 1 << 28;
//constexpr long long mod = 1000000007LL;
//constexpr long long mod = 998244353LL;

using namespace std;
typedef unsigned long long ull;
typedef long long ll;

int main()
{
	/*
	cin.tie(nullptr);
	ios::sync_with_stdio(false);
	*/
	int kkt = 89;
	while (kkt) {
		int n; scanf("%d", &n); if (n == 0) break;
		vector<string> vs(n); for (int i = 0; i < n; i++) cin >> vs[i];
		ll mx = INF;
		ll mn = -INF;
		int state = 0;
		for (int i = 0; i < n; i++) {
			if (vs[i] == "x") {
				if (i == 0) {
					if (vs[i + 1] == "x") {
						state = -1;
						break;
					}
					if(i % 2 == 0) chmin(mx, stoll(vs[i + 1]) - 1);
					else chmax(mn, stoll(vs[i + 1]) + 1);
				}
				else if (i == n - 1) {
					if (vs[i - 1] == "x") {
						state = -1;
						break;
					}
					if (i % 2 == 0) chmin(mx, stoll(vs[i - 1]) - 1);
					else chmax(mn, stoll(vs[i - 1]) + 1);
				}
				else {
					if (vs[i + 1] == "x") {
						state = -1;
						break;
					}
					if (i % 2 == 0) chmin(mx, stoll(vs[i + 1]) - 1);
					else chmax(mn, stoll(vs[i + 1]) + 1);

					if (vs[i - 1] == "x") {
						state = -1;
						break;
					}
					if (i % 2 == 0) chmin(mx, stoll(vs[i - 1]) - 1);
					else chmax(mn, stoll(vs[i - 1]) + 1);
				}
			}
			else {
				if (i == 0) {
					if (vs[i + 1] != "x") {
						if (i % 2 == 0) {
							if (stoll(vs[i]) >= stoll(vs[i + 1])) {
								state = -1;
								break;
							}
						}
						else {
							if (stoll(vs[i]) <= stoll(vs[i + 1])) {
								state = -1;
								break;
							}
						}
					}
				}
				else if (i == n - 1) {
					if (vs[i - 1] != "x") {
						if (i % 2 == 0) {
							if (stoll(vs[i]) >= stoll(vs[i - 1])) {
								state = -1;
								break;
							}
						}
						else {
							if (stoll(vs[i]) <= stoll(vs[i - 1])) {
								state = -1;
								break;
							}
						}
					}
				}
				else {
					if (vs[i + 1] != "x") {
						if (i % 2 == 0) {
							if (stoll(vs[i]) >= stoll(vs[i + 1])) {
								state = -1;
								break;
							}
						}
						else {
							if (stoll(vs[i]) <= stoll(vs[i + 1])) {
								state = -1;
								break;
							}
						}
					}
					if (vs[i - 1] != "x") {
						if (i % 2 == 0) {
							if (stoll(vs[i]) >= stoll(vs[i - 1])) {
								state = -1;
								break;
							}
						}
						else {
							if (stoll(vs[i]) <= stoll(vs[i - 1])) {
								state = -1;
								break;
							}
						}
					}

				}
			}
		}
		if (state == -1 or mn > mx) puts("none");
		else if (mx == mn) printf("%lld\n", mx);
		else puts("ambiguous");
	}
	return 0;

}



Measured memory_bytes: 3384