#include<bits/stdc++.h>

using namespace std;

/// Typedef
typedef long long           ll;
typedef unsigned long       ul;
typedef unsigned long long  ull;
typedef vector<int>         vi;
typedef vector<vi>          vvi;
typedef vector<ll>          vll;
typedef pair<int,int>       pii;
typedef pair<ll,ll>         pll;
typedef vector< pii >       vii;

#define pb                  push_back
#define ppb                 pop_back
#define MP                  make_pair
#define ff                  first
#define ss                  second
#define sf                  scanf
#define pf                  printf
#define SQR(x)              ((x)*(x))
#define loop(i, y)          for(int i=0; i<int(y); i++)
#define FOR(i, x, y)        for(int i=int(x); i<=int(y); i++)
#define ROF(i, x, y)        for(int i=int(x); i>=int(y); i--)
#define ALL(c)              c.begin(), c.end()
#define SZ(c)               int(c.size())
#define CLR(x, y)           memset(x, y, sizeof(x))
#define READ(f)             freopen(f, "r", stdin)
#define WRITE(f)            freopen(f, "w", stdout)
#define FastIO              ios_base::sync_with_stdio(false)
#define tr(it, container)   for(auto it = container.begin(); it != container.end(); it++)
#define sci(x)              scanf("%d", &x)
#define scii(x, y)          scanf("%d %d", &x, &y)
#define sciii(x, y, z)      scanf("%d %d %d", &x, &y, &z)
#define scl(x)              scanf("%lld", &x)
#define scll(x, y)          scanf("%lld %lld", &x, &y)
#define sclll(x, y, z)      scanf("%lld %lld %lld", &x, &y, &z)
#define bitCheck(N,in)      ((bool)(N&(1<<(in))))
#define bitOff(N,in)        (N&(~(1LL<<(in))))
#define bitOn(N,in)         (N|(1LL<<(in)))
#define bitFlip(a,k)        (a^(1LL<<(k)))
#define unq(v)              sort(all(v)), (v).erase(unique(all(v)),v.end())
#define common(a,b)         sort(all(a)), sort(all(b)), a.erase(set_intersection(all(a),all(b),a.begin()),a.end())
#define uncommon(a,b)       sort(all(a)), sort(all(b)), a.erase(set_symmetric_difference(all(a),all(b),a.begin()),a.end())
#define dbg(x)              cout<<#x<<" = "<<x<<endl;

int main()
{
    int n, k=0;
    while(sci(n)==1){
        int arr[1002]={0}, mark[20002]={0}, flag=0;
        for(int i=1; i<=n; i++){
            sci(arr[i]);
            if(arr[i]<=arr[i-1]){
                flag=1;
            }
        }

        if(flag==0){
            for(int i=1; i<=n; i++){
                for(int j=i; j<=n; j++){
                    if(mark[arr[i]+arr[j]]!=0){
                        flag=1;
                    }
                    mark[arr[i]+arr[j]]=1;
                }
            }
        }
        if(!flag){
            printf("Case #%d: It is a B2-Sequence.\n\n", ++k);
        }
        else printf("Case #%d: It is not a B2-Sequence.\n\n", ++k);
    }
    return 0;
}