#pragma GCC optimize("Ofast")
#include "bits/stdc++.h"

// Begin Header {{{
using namespace std;

#ifndef DEBUG
#define dump(...)
#endif

#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
#define rep(i, b, e) for (intmax_t i = (b), i##_limit = (e); i < i##_limit; ++i)
#define repc(i, b, e) for (intmax_t i = (b), i##_limit = (e); i <= i##_limit; ++i)
#define repr(i, b, e) for (intmax_t i = (b), i##_limit = (e); i >= i##_limit; --i)
#define var(Type, ...) Type __VA_ARGS__; input(__VA_ARGS__)

constexpr size_t    operator""_zu(unsigned long long value) { return value; };
constexpr intmax_t  operator""_jd(unsigned long long value) { return value; };
constexpr uintmax_t operator""_ju(unsigned long long value) { return value; };

constexpr int INF = 0x3f3f3f3f;
constexpr intmax_t LINF = 0x3f3f3f3f3f3f3f3f_jd;

template <class T, class Compare = less<>>
using MaxHeap = priority_queue<T, vector<T>, Compare>;
template <class T, class Compare = greater<>>
using MinHeap = priority_queue<T, vector<T>, Compare>;

inline void input() {}
template <class Head, class... Tail>
inline void input(Head&& head, Tail&&... tail) {
    cin >> head;
    input(forward<Tail>(tail)...);
}

template <class Container, class Value = typename Container::value_type,
enable_if_t<!is_same<Container, string>::value, nullptr_t> = nullptr>
inline istream& operator>>(istream &is, Container &vs) {
    for (auto &v: vs) is >> v;
    return is;
}

template <class T, class U>
inline istream& operator>>(istream &is, pair<T, U> &p) {
    is >> p.first >> p.second;
    return is;
}

inline void output() { cout << "\n"; }
template <class Head, class... Tail>
inline void output(Head&& head, Tail&&... tail) {
    cout << head;
    if (sizeof...(tail)) cout << " ";
    output(forward<Tail>(tail)...);
}

template <class Container, class Value = typename Container::value_type,
enable_if_t<!is_same<Container, string>::value, nullptr_t> = nullptr>
inline ostream& operator<<(ostream &os, const Container &vs) {
    static constexpr const char *delim[] = {" ", ""};
    for (auto it = begin(vs); it != end(vs); ++it) {
        os << delim[it == begin(vs)] << *it;
    }
    return os;
}

template <class Iterator>
inline void join(const Iterator &Begin, const Iterator &End, const string &delim = "\n", const string &last = "\n") {
    for (auto it = Begin; it != End; ++it) {
        cout << ((it == Begin) ? "" : delim) << *it;
    }
    cout << last;
}

template <class T>
inline vector<T> makeVector(const T &init_value, size_t sz) {
    return vector<T>(sz, init_value);
}

template <class T, class... Args>
inline auto makeVector(const T &init_value, size_t sz, Args... args) {
    return vector<decltype(makeVector<T>(init_value, args...))>(sz, makeVector<T>(init_value, args...));
}

template <class Func>
class FixPoint : Func {
public:
    explicit constexpr FixPoint(Func&& f) noexcept : Func(forward<Func>(f)) {}

    template <class... Args>
    constexpr decltype(auto) operator()(Args&&... args) const {
        return Func::operator()(*this, std::forward<Args>(args)...);
    }
};

template <class Func>
static inline constexpr decltype(auto) makeFixPoint(Func&& f) noexcept {
    return FixPoint<Func>{forward<Func>(f)};
}

template <class Container>
struct reverse_t {
    Container &c;
    reverse_t(Container &c) : c(c) {}
    auto begin() { return c.rbegin(); }
    auto end() { return c.rend(); }
};

template <class Container>
auto reversed(Container &c) {
    return reverse_t<Container>(c);
}

template <class T>
inline bool chmax(T &a, const T &b) noexcept {
    return b > a && (a = b, true);
}

template <class T>
inline bool chmin(T &a, const T &b) noexcept {
    return b < a && (a = b, true);
}

template <class T>
inline T diff(const T &a, const T &b) noexcept {
    return a < b ? b - a : a - b;
}

void operator|=(vector<bool>::reference lhs, const bool rhs) {
    lhs = lhs | rhs;
}

void ioinit() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout << fixed << setprecision(10);
    cerr << fixed << setprecision(10);
    clog << fixed << setprecision(10);
}
// }}} End Header

// FenwickTree {{{
template <class T>
struct FenwickTree {
    vector<T> ft;
    const size_t SIZE;

    explicit FenwickTree(size_t n) : ft(n + 5, 0), SIZE(1 << (__lg(n + 5) + 1)) {}

    void add(int i, const T& v) {
        for (++i; i < ft.size(); i += i & -i) ft[i] += v;
    }

    // [0, i]
    T sum(int i) const {
        T ret = 0;
        for (++i; i > 0; i -= i & -i) ret += ft[i];
        return ret;
    }

    // [s, t]
    T sum(int s, int t) const {
        if (s > t) swap(s, t);
        return sum(t) - sum(s - 1);
    }

    size_t lower_bound(T v) const {
        if (v <= 0) return 0;
        T x = 0;
        for (size_t k = SIZE; k > 0; k >>= 1) {
            if (x + k < ft.size() && ft[x + k] < v) {
                v -= ft[x + k];
                x += k;
            }
        }
        return x;
    }
};
// }}}

int main() {
    ioinit();

    var(size_t, N);
    var(intmax_t, X);

    vector<intmax_t> ss(N + 1);
    repc(i, 1, N) input(ss[i]);

    FenwickTree<intmax_t> ft(N + 1);
    repc(i, 1, N) {
        ft.add(i, X - ss[i]);
    }

    repc(i, 1, N) {
        intmax_t S = ft.sum(0, i - 1) + ft.sum(i + 1, N + 1);
        if (X - ss[i] / 2 + S == X) {
            return output(S), 0;
        }
    }
    return 0;
}