import java.util.*;
import java.io.*;

public class Main{
    static final Reader sc = new Reader();
    static final PrintWriter out = new PrintWriter(System.out,false);

    public static void main(String[] args) throws Exception {
    	
    	while(true){
    		int n = sc.nextInt();
    		if(n==0){
    			break;
    		}
    		int under = Integer.MIN_VALUE/2;
    		int top = Integer.MAX_VALUE/2;
    		String[] s = new String[n];
    		for(int i=0;i<n;i++){
    			s[i] = sc.next();
    		}
    		boolean flag = false;
    		boolean none = false;
    		for(int i=0;i<n;i++){
    			if(s[i].charAt(0)=='x'){
    				if(flag){
    					none = true;
    					break;
    				}
    				else{
    					flag = true;
    				}
    			}
    			else{
    				flag = false;
    			}
    		}
    		if(none){
    			out.println("none");
    		}
    		else{
    			flag = false;
    			for(int i=0;i<n;i++){
    				if(s[i].charAt(0)=='x'){
    					if(flag){
    						if(i==0){
    							under = Math.max(under,Integer.parseInt(s[i+1]));
    						}
    						else if(i==n-1){
    							under = Math.max(under,Integer.parseInt(s[i-1]));
    						}
    						else{
    							under = Math.max(under,Math.max(Integer.parseInt(s[i-1]),Integer.parseInt(s[i+1])));
    						}
    					}
    					else{
    						if(i==n-1){
    							top = Math.min(top,Integer.parseInt(s[i-1]));
    						}
    						else if(i==0){
    							top = Math.min(top,Integer.parseInt(s[i+1]));
    						}
    						else{
    							top = Math.min(top,Math.min(Integer.parseInt(s[i-1]),Integer.parseInt(s[i+1])));
    						}
    					}
    				}
    				else if(flag){
    						if(i==n-1){
    							if(s[i-1].charAt(0)!='x'){
    								int a = Integer.parseInt(s[i-1]);
    								int b = Integer.parseInt(s[i]);
    								if(a>=b){
    									none = true;
    								}
    							}
    						}
    						else{
    							if(s[i-1].charAt(0)!='x'){
    								int a = Integer.parseInt(s[i-1]);
    								int b = Integer.parseInt(s[i]);
    								if(a>=b){
    									none = true;
    								}
    							}
    							if(s[i+1].charAt(0)!='x'){
    								int a = Integer.parseInt(s[i+1]);
    								int b = Integer.parseInt(s[i]);
    								if(a>=b){
    									none = true;
    								}
    							}
    						}
    					}
    					else{
    						if(i==0){
    							if(s[i+1].charAt(0)!='x'){
    								int a = Integer.parseInt(s[i+1]);
    								int b = Integer.parseInt(s[i]);
    								if(a<=b){
    									none = true;
    								}
    							}
    						}
    						else if(i==n-1){
    							if(s[i-1].charAt(0)!='x'){
    								int a = Integer.parseInt(s[i-1]);
    								int b = Integer.parseInt(s[i]);
    								if(a<=b){
    									none = true;
    								}
    							}
    						}
    						else{
    							if(s[i+1].charAt(0)!='x'){
    								int a = Integer.parseInt(s[i+1]);
    								int b = Integer.parseInt(s[i]);
    								if(a<=b){
    									none = true;
    								}
    							}
    							if(s[i-1].charAt(0)!='x'){
    								int a = Integer.parseInt(s[i-1]);
    								int b = Integer.parseInt(s[i]);
    								if(a<=b){
    									none = true;
    								}
    							}
    						}
    					}
    					flag = !flag;
    				}
    			if(none){
    				out.println("none");
    			}
    			else if(top-under == 2){
    				out.println(under+1);
    			}
    			else if(top-under > 2){
    				out.println("ambiguous");
    			}
    			else{
    				out.println("none");
    			}
    		}
    		out.flush();
    	}

        sc.close();
        out.close();
    }

    static void trace(Object... o) { System.out.println(Arrays.deepToString(o));}
}

class Reader {

    private final InputStream in;
    private final byte[] buf = new byte[1024];
    private int ptr = 0;
    private int buflen = 0;

    public Reader() { this(System.in);}
    public Reader(InputStream source) { this.in = source;}

    private boolean hasNextByte() {
        if (ptr < buflen) return true;
        ptr = 0;
        try{
            buflen = in.read(buf);
        }catch (IOException e) {e.printStackTrace();}
        if (buflen <= 0) return false;
        return true;
    }

    private int readByte() { if (hasNextByte()) return buf[ptr++]; else return -1;}

    private boolean isPrintableChar(int c) { return 33 <= c && c <= 126;}

    private void skip() { while(hasNextByte() && !isPrintableChar(buf[ptr])) ptr++;}

    public boolean hasNext() {skip(); return hasNextByte();}

    public String next() {
        if (!hasNext()) throw new NoSuchElementException();
        StringBuilder sb = new StringBuilder();
        int b = readByte();
        while (isPrintableChar(b)) {
            sb.appendCodePoint(b);
            b = readByte();
        }
        return sb.toString();
    }

    public long nextLong() {
        if (!hasNext()) throw new NoSuchElementException();
        boolean minus = false;
        long num = readByte();

        if(num == '-'){
            num = 0;
            minus = true;
        }else if (num < '0' || '9' < num){
            throw new NumberFormatException();
        }else{
            num -= '0';
        }

        while(true){
            int b = readByte();
            if('0' <= b && b <= '9')
                num = num * 10 + (b - '0');
            else if(b == -1 || !isPrintableChar(b))
                return minus ? -num : num;
            else
                throw new NoSuchElementException();
        }
    }

    public int nextInt() {
        long num = nextLong();
        if (num < Integer.MIN_VALUE || Integer.MAX_VALUE < num)
            throw new NumberFormatException();
        return (int)num;
    }

    public double nextDouble() {
        return Double.parseDouble(next());
    }

    public char nextChar() {
        if (!hasNext()) throw new NoSuchElementException();
        return (char)readByte();
    }

    public String nextLine() {
        while (hasNextByte() && (buf[ptr] == '\n' || buf[ptr] == '\r')) ptr++;
        if (!hasNextByte()) throw new NoSuchElementException();

        StringBuilder sb = new StringBuilder();
        int b = readByte();
        while (b != '\n' && b != '\r') {
            sb.appendCodePoint(b);
            b = readByte();
        }

        return sb.toString();
    }

    public int[] nextIntArray(int n) {
        int[] res = new int[n];
        for (int i=0; i<n; i++) res[i] = nextInt();
        return res;
    }

    public char[] nextCharArray(int n) {
        char[] res = new char[n];
        for (int i=0; i<n; i++) res[i] = nextChar();
        return res;
    }

    public void close() {try{ in.close();}catch(IOException e){ e.printStackTrace();}};
}

Measured memory_bytes: 33280