//include
//------------------------------------------
#include <vector>
#include <list>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <fstream>
#include <complex>
#include <math.h>

using namespace std;

//conversion
//------------------------------------------
inline long toInt(string s) {int v; istringstream sin(s);sin>>v;return v;}
inline long toLong(string s) {long v; istringstream sin(s);sin>>v;return v;}
template<class T> inline string toString(T x) {ostringstream sout;sout<<x;return sout.str();}

//math
//-------------------------------------------
template<class T> inline T sqr(T x) {return x*x;}

//typedef
//------------------------------------------
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef pair<long, long> PLL;
typedef long long LL;
//container util
//------------------------------------------
#define ALL(a)  (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define SZ(a) int((a).size())
#define EACH(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())

//repetition
//------------------------------------------
#define FOR(i,a,b) for(long i=(a);i<(b);++i)
#define REP(i,n) FOR(i,0,n)

//constant
//--------------------------------------------

//clear memory
#define CLR(a) memset((a), 0 ,sizeof(a))

const long double EPS = 1e-8;
const long INF = 1e10;

int main(){
	int N;
	while(cin>>N&&N){
		long b[1002];
		b[0]=INF+1;
		long maxx=INF,minx=-INF;
		REP(i,N){
			string a;
			cin>>a;
			if(a=="x"){
				b[i+1]=((i+1)%2)?-INF:INF;
			}else{
				b[i+1]=toLong(a);
			}
		}
		b[N+1]=((N+1)%2)?-INF-1:INF+1;
		bool flag=true;
		FOR(i,1,N+1){
			if(i%2){
				if(b[i]>=b[i-1]||b[i]>=b[i+1]){
					flag=false;
					break;
				}else if(b[i]==-INF){
					if(b[i-1]==INF||b[i+1]==INF)flag=false;
					maxx=min(maxx,min(b[i-1],b[i+1]));
				}
			}else{
				if(b[i]<=b[i-1]||b[i]<=b[i+1]){
					flag=false;
					break;
				}else if(b[i]==INF){
					if(b[i-1]==-INF||b[i+1]==-INF)flag=false;
					minx=max(minx,max(b[i-1],b[i+1]));
				}
			}
		}
		if(!flag||maxx-minx<=1){
			cout<<"none"<<endl;
		}else{
			if(maxx-minx==2)cout<<(maxx+minx)/2<<endl;
			else cout<<"ambiguous"<<endl;
			//cout<<maxx<<" "<<minx<<endl;
		}
	}
	return 0;
}