#include <bits/stdc++.h>
// created [2020/01/17] 21:38:53
#pragma GCC diagnostic ignored "-Wsign-compare"
#pragma GCC diagnostic ignored "-Wsign-conversion"

using i32   = int32_t;
using i64   = int64_t;
using u32   = uint32_t;
using u64   = uint64_t;
using uint  = unsigned int;
using usize = std::size_t;
using ll    = long long;
using ull   = unsigned long long;
using ld    = long double;
template<typename T, usize n>
using arr = T (&)[n];
template<typename T, usize n>
using c_arr = const T (&)[n];
template<typename T> constexpr T popcount(const T u) { return u ? static_cast<T>(__builtin_popcountll(static_cast<u64>(u))) : static_cast<T>(0); }
template<typename T> constexpr T log2p1(const T u) { return u ? static_cast<T>(64 - __builtin_clzll(static_cast<u64>(u))) : static_cast<T>(0); }
template<typename T> constexpr T msbp1(const T u) { return log2p1(u); }
template<typename T> constexpr T lsbp1(const T u) { return __builtin_ffsll(u); }
template<typename T> constexpr T clog(const T u) { return u ? log2p1(u - 1) : static_cast<T>(u); }
template<typename T> constexpr bool ispow2(const T u) { return u and (static_cast<u64>(u) & static_cast<u64>(u - 1)) == 0; }
template<typename T> constexpr T ceil2(const T u) { return static_cast<T>(1) << clog(u); }
template<typename T> constexpr T floor2(const T u) { return u == 0 ? static_cast<T>(0) : static_cast<T>(1) << (log2p1(u) - 1); }
template<typename T> constexpr bool btest(const T mask, const usize ind) { return static_cast<bool>((static_cast<u64>(mask) >> ind) & static_cast<u64>(1)); }
template<typename T> void bset(T& mask, const usize ind) { mask |= (static_cast<T>(1) << ind); }
template<typename T> void breset(T& mask, const usize ind) { mask &= ~(static_cast<T>(1) << ind); }
template<typename T> void bflip(T& mask, const usize ind) { mask ^= (static_cast<T>(1) << ind); }
template<typename T> void bset(T& mask, const usize ind, const bool b) { (b ? bset(mask, ind) : breset(mask, ind)); }
template<typename T> constexpr T bcut(const T mask, const usize ind) { return ind == 0 ? static_cast<T>(0) : static_cast<T>((static_cast<u64>(mask) << (64 - ind)) >> (64 - ind)); }
template<typename T> bool chmin(T& a, const T& b) { return (a > b ? a = b, true : false); }
template<typename T> bool chmax(T& a, const T& b) { return (a < b ? a = b, true : false); }
constexpr unsigned int mod                  = 1000000007;
template<typename T> constexpr T inf_v      = std::numeric_limits<T>::max() / 4;
template<typename Real> constexpr Real pi_v = Real{3.141592653589793238462643383279502884};
auto mfp = [](auto&& f) { return [=](auto&&... args) { return f(f, std::forward<decltype(args)>(args)...); }; };

template<typename T>
T in()
{
    T v;
    return std::cin >> v, v;
}
template<typename T, typename Uint, usize n, usize i>
T in_v(typename std::enable_if<(i == n), c_arr<Uint, n>>::type) { return in<T>(); }
template<typename T, typename Uint, usize n, usize i>
auto in_v(typename std::enable_if<(i < n), c_arr<Uint, n>>::type& szs)
{
    const usize s = (usize)szs[i];
    std::vector<decltype(in_v<T, Uint, n, i + 1>(szs))> ans(s);
    for (usize j = 0; j < s; j++) { ans[j] = in_v<T, Uint, n, i + 1>(szs); }
    return ans;
}
template<typename T, typename Uint, usize n>
auto in_v(c_arr<Uint, n> szs) { return in_v<T, Uint, n, 0>(szs); }
template<typename... Types>
auto in_t() { return std::tuple<std::decay_t<Types>...>{in<Types>()...}; }
struct io_init
{
    io_init()
    {
        std::cin.tie(nullptr), std::ios::sync_with_stdio(false);
        std::cout << std::fixed << std::setprecision(20);
    }
    void clear()
    {
        std::cin.tie(), std::ios::sync_with_stdio(true);
    }
} io_setting;

template<typename T>
int out(const T& v) { return std::cout << v, 0; }
template<typename T>
int out(const std::vector<T>& v)
{
    for (usize i = 0; i < v.size(); i++) {
        if (i > 0) { std::cout << ' '; }
        out(v[i]);
    }
    return std::cout << "\n", 0;
}
template<typename T1, typename T2>
int out(const std::pair<T1, T2>& v) { return out(v.first), std::cout << ' ', out(v.second), 0; }
template<typename T, typename... Args>
int out(const T& v, const Args... args) { return out(v), std::cout << ' ', out(args...), 0; }
template<typename... Args>
int outln(const Args... args) { return out(args...), std::cout << '\n', 0; }
template<typename... Args>
void outel(const Args... args) { return out(args...), std::cout << std::endl, 0; }
#    define SHOW(...) static_cast<void>(0)
constexpr ull TEN(const usize n) { return n == 0 ? 1ULL : TEN(n - 1) * 10ULL; }

template<typename T, typename Uint, usize n, usize i>
auto make_v(typename std::enable_if<(i == n), c_arr<Uint, n>>::type, const T& v = T{}) { return v; }
template<typename T, typename Uint, usize n, usize i>
auto make_v(typename std::enable_if<(i < n), c_arr<Uint, n>>::type szs, const T& v = T{})
{
    const usize s = (usize)szs[i];
    return std::vector<decltype(make_v<T, Uint, n, i + 1>(szs, v))>(s, make_v<T, Uint, n, i + 1>(szs, v));
}
template<typename T, typename Uint, usize n>
auto make_v(c_arr<Uint, n> szs, const T& t = T{}) { return make_v<T, Uint, n, 0>(szs, t); }

template<typename Element = ll>
class fenwick
{
public:
    using value_type = Element;
    fenwick(const usize sz, const value_type initial = value_type{}) : sz{sz}, cap{ceil2(sz)}, val(cap + 1, 0)
    {
        if (initial != value_type{}) {
            std::fill(val.begin() + 1, val.end(), initial);
            for (usize x = 1; x < cap; x++) { val[x + (x & -x)] += val[x]; }
        }
    }
    template<typename InIt>
    fenwick(const InIt first, const InIt last) : sz{static_cast<usize>(std::distance(first, last))}, cap{ceil2(sz)}, val(cap + 1, 0)
    {
        std::copy(first, last, val.begin() + 1);
        for (usize x = 1; x < cap; x++) { val[x + (x & -x)] += val[x]; }
    }
    void add(const usize a, const value_type& v)
    {
        assert(a < sz);
        for (usize ind = a + 1; ind <= cap; ind += ind & (-ind)) { val[ind] += v; }
    }
    value_type sum(const usize a) const
    {
        assert(a <= sz);
        value_type sum{};
        for (usize ind = a; ind != 0; ind &= ind - 1) { sum += val[ind]; }
        return sum;
    }
    value_type sum(const usize l, const usize r) const { return assert(l < r), assert(r <= sz), sum(r) - sum(l); }
    usize size() const { return sz; }
    friend std::ostream& operator<<(std::ostream& os, const fenwick& fw)
    {
        os << "[";
        for (usize i = 0; i < fw.sz; i++) { os << fw.sum(i, i + 1) << (i + 1 == fw.sz ? "" : ","); }
        return (os << "]\n");
    }

private:
    const usize sz, cap;
    std::vector<value_type> val;
};
int main()
{
    const int N  = in<int>();
    const ll X   = in<ll>();
    const auto a = in_v<ll>({N});
    auto s       = a;
    for (int i = 1; i < N; i++) { s[i] += s[i - 1]; }
    auto sum = [&](const int i, const int j) { return s[j - 1] - (i == 0 ? 0LL : s[i - 1]); };
    std::vector<int> right(N + 1);  // a[i,right[i]) <= X
    for (int i = 0; i < N; i++) {
        int inf = i, sup = N + 1;
        while (sup - inf > 1) {
            const int mid                 = (inf + sup) / 2;
            (sum(i, mid) > X ? sup : inf) = mid;
        }
        right[i] = inf;
    }
    std::vector<int> left(N + 1);  // a[left[i],i) <= X
    for (int i = 1; i <= N; i++) {
        int inf = -1, sup = i;
        while (sup - inf > 1) {
            const int mid                 = (inf + sup) / 2;
            (sum(mid, i) > X ? inf : sup) = mid;
        }
        left[i] = sup;
    }
    SHOW(left, right);
    auto win = make_v({N, N + 1}, 0);                            // a[l,r)から先手が勝てるか
    std::vector<fenwick<int>> lbit(N + 1, fenwick<int>(N + 1));  // lbit[r][l] = win[l][r]
    std::vector<fenwick<int>> rbit(N + 1, fenwick<int>(N + 1));  // rbit[l][r] = win[l][r]
    for (int l = 0; l < N; l++) {
        win[l][l] = 1;
        lbit[l].add(l, 1);
        rbit[l].add(l, 1);
    }
    for (int l = N - 2; l >= 0; l--) {
        for (int r = l + 2; r <= N; r++) {        // a[l,r)
            const int R = std::min(r, right[l]);  // 取れるのはa[l],a[l+1],...,a[R-1]まで
            const int L = std::max(l, left[r]);   // 取れるのはa[r-1],a[r-2],...,a[L]まで
            SHOW(l, r, R, L);
            const int rs = lbit[r].sum(l + 1, R + 1);  // 遷移先は[l+1,r),[l+2,r),...,[R,r)
            const int ls = rbit[l].sum(L, r);          // 遷移先は[l,L),[l,L+1),...,[l,r-1)
            SHOW(rs, ls);
            win[l][r] = (rs < R - l or ls < r - L);
            lbit[r].add(l, win[l][r]);
            rbit[l].add(r, win[l][r]);
        }
    }
    SHOW(win, lbit, rbit);
    outln(win[0][N] ? "A" : "B");
    return 0;
}