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