hoj12839

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#define INF 1000000100
#define MAX 1000000200

using namespace std;

char a[15];
int b[1005];

int main()
{
    int N;
    while(scanf("%d", &N), N)
    {
        int num = 0;
        int judge = 0; //1 唯一存在 2 不存在 3 很多种
        int l = -INF, r = INF;
        b[0] = 0;
        for(int i = 1; i <= N; i++) { //把对应的字符串转化成数字
            int s;
            scanf("%s", a);
            if(a[0] == ‘x‘) b[i] = INF;
            else {
                    s = 0;
                    int j;
                    if(a[0] == ‘-‘) j = 1;
                    else j = 0;
                    for(j = j; a[j]; j++) {
                        s *= 10;
                        s += a[j] - ‘0‘;
                    }
                    if(a[0] == ‘-‘) b[i] = -s;
                    else b[i] = s;
            }
        }
        b[0] = MAX;
        for(int i = 1; i <= N && judge != 2; i++) {
            if(b[i] == INF && b[i-1] == INF) judge = 2;
            else if(b[i] == INF && b[i-1] != INF) {
                if(i%2) r = min(r, b[i-1]-1); //当前是奇数位 x比前面一个数小 那么x的上限应该为l与前面一个数中较小的
                else l = max(l, b[i-1]+1); //当前是偶数位 x比前面的一个数大 那么x的下限应该是x和前面一个数较大的
            }
            else if(b[i] != INF && b[i-1] == INF) {
                if(i%2) l = max(l, b[i]+1);
                else r = min(r, b[i]-1);
            }
            else {
                if(i%2 && b[i] >= b[i-1] || !(i%2) && b[i] <= b[i-1]) judge = 2;
            }
        }
        if(judge == 2 || l > r) printf("none\n");
        else if(l == r) printf("%d\n", l);
        else if(l < r) printf("ambiguous\n");
    }
    return 0;
}