#include<bits/stdc++.h>
using namespace std;
#define ALL(x) begin(x),end(x)
#define rep(i,n) for(int i=0;i<(n);i++)
#define debug(v) cout<<#v<<":";for(auto x:v){cout<<x<<' ';}cout<<endl;
#define mod 998244353
using ll=long long;
const int INF=1000000000;
const ll LINF=1001002003004005006ll;
int dx[]={1,0,-1,0},dy[]={0,1,0,-1};
template<class T>bool chmax(T &a,const T &b){if(a<b){a=b;return true;}return false;}
template<class T>bool chmin(T &a,const T &b){if(b<a){a=b;return true;}return false;}

struct IOSetup{
    IOSetup(){
        cin.tie(0);
        ios::sync_with_stdio(0);
        cout<<fixed<<setprecision(12);
    }
} iosetup;
 
template<typename T>
ostream &operator<<(ostream &os,const vector<T>&v){
    for(int i=0;i<(int)v.size();i++) os<<v[i]<<(i+1==(int)v.size()?"":" ");
    return os;
}
template<typename T>
istream &operator>>(istream &is,vector<T>&v){
    for(T &x:v)is>>x;
    return is;
}

template<typename Monoid>
struct SegmentTree{
    using F=function<Monoid(Monoid,Monoid)>;

    private:
    int sz;
    vector<Monoid> seg;

    Monoid query(int a,int b,int k,int l,int r){
        if(a<=l and r<=b)   return seg[k];
        if(b<=l or r<=a)    return M0;
        Monoid L=query(a,b,2*k,l,(l+r)/2);
        Monoid R=query(a,b,2*k+1,(l+r)/2,r);
        return f(L,R);
    }
    template<typename C>
    int find_first(int a,const C &check,Monoid &acc,int k,int l,int r){
        if(k>=sz){
            acc=f(acc,seg[k]);
            if(check(acc))  return -1;
            else            return k-sz;
        }
        int m=(l+r)/2;
        if(m<=a) return find_first(a,check,acc,2*k+1,m,r);
        if(a<=l and check(f(acc,seg[k]))){
            acc=f(acc,seg[k]);
            return -1;
        }
        int x=find_first(a,check,acc,2*k+0,l,m);
        if(x>=0) return x;
        return find_first(a,check,acc,2*k+1,m,r);
    }
    template<typename C>
    int find_last(int b,const C &check,Monoid &acc,int k,int l,int r){
        if(k>=sz){
            acc=f(acc,seg[k]);
            if(check(acc))  return -1;
            else            return k-sz+1;//ここはfalse, +1した位置はtrue
        }
        int m=(l+r)/2;
        if(b<=m) return find_last(b,check,acc,2*k,l,m);
        if(r<=b and check(f(acc,seg[k]))){
            acc=f(acc,seg[k]);
            return -1;
        }
        int x=find_last(b,check,acc,2*k+1,m,r);
        if(x>=0) return x;
        return find_last(b,check,acc,2*k,l,m);
    }

    public:

    F f;
    Monoid M0;// モノイドの元
    SegmentTree(int n,F f,Monoid M0):f(f),M0(M0){
        sz=1;
        while(sz<n)sz<<=1;
        seg.assign(2*sz,M0);
    }
    void set(int k,Monoid x){
        seg[k+sz]=x;
    }
    void build(){
        for(int k=sz-1;k>0;k--) seg[k]=f(seg[2*k],seg[2*k+1]);
    }
    void update(int k,Monoid x){
        k+=sz;
        seg[k]=x;
        k>>=1;
        for(;k;k>>=1) seg[k]=f(seg[2*k],seg[2*k+1]);
    }
    Monoid query(int a,int b){
        return query(a,b,1,0,sz);
    }

    // http://codeforces.com/contest/914/submission/107505449
    // max x, check(query(a, x)) = true 
    template<typename C>
    int find_first(int a,const C &check){
        Monoid val=M0;
        return find_first(a,check,val,1,0,sz);
    }
    // http://codeforces.com/contest/914/submission/107505582
    // min x, check(query(x, b)) = true
    template<typename C>
    int find_last(int b,C &check){
        Monoid val=M0;
        return find_last(b,check,val,1,0,sz);
    }
};

int func(int a,int b){return a+b;}

vector<bitset<5001>> dp(5001);

vector<SegmentTree<int>> seg_l(5001,SegmentTree<int>(5001,func,0)),seg_r(5001,SegmentTree<int>(5001,func,0));

void solve(){
    int n;ll x;cin>>n>>x;
    vector<ll> v(n);
    cin>>v;

    vector<ll> s(n);
    s[0]=v[0];
    for(int i=1;i<n;i++) s[i]=s[i-1]+v[i];
    rep(i,n) seg_l[i].set(i+1,1);
    rep(i,n) seg_r[i+1].set(i,1);
    rep(i,n+1) seg_l[i].build();
    rep(i,n+1) seg_r[i].build();

    for(int w=2;w<=n;w++){
        for(int l=0;l+w<=n;l++){
            int r=l+w;// [l,r)
            bool win=false;
            // left
            {
                ll offset=(l==0?0:s[l-1]);
                int ri=lower_bound(begin(s),end(s),offset+x+1)-begin(s);
                // can take [l,r)
                if(seg_l[l].query(l,ri)) win=true;
            }
            // right
            {
                int li=lower_bound(begin(s),end(s),s[r-1]-x+1)-begin(s);
                if(seg_r[r].query(li,r)) win=true;
            }
            dp[l][r]=win;
            if(!win){
                seg_l[l].update(r,1);
                seg_r[r].update(l,1);
            }
        }
    }
    cout<<(dp[0][n]?"A":"B")<<endl;
}

void naive(){
    int n;ll x;cin>>n>>x;
    vector<ll> v(n);
    cin>>v;



    for(int w=2;w<=n;w++){
        for(int l=0;l+w<=n;l++){
            int r=l+w;// [l,r)
            bool win=false;
            // left
            {
                ll s=v[l];
                for(int i=l+1;i<r and s<=x;i++){
                    if(!dp[i][r]) win=true;
                    s+=v[i];
                }
            }
            // right
            {
                ll s=v[r-1];
                for(int i=r-1;i>l and s<=x;i--){
                    if(!dp[l][i]) win=true;
                    s+=v[i-1];
                }
            }
            dp[l][r]=win;
        }
    }
    cout<<(dp[0][n]?"A":"B")<<endl;
}

signed main(){
    // naive();
    solve();
    return 0;
}