#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 > using MaxHeap = priority_queue, Compare>; template > using MinHeap = priority_queue, Compare>; inline void input() {} template inline void input(Head&& head, Tail&&... tail) { cin >> head; input(forward(tail)...); } template ::value, nullptr_t> = nullptr> inline istream& operator>>(istream &is, Container &vs) { for (auto &v: vs) is >> v; return is; } template inline istream& operator>>(istream &is, pair &p) { is >> p.first >> p.second; return is; } inline void output() { cout << "\n"; } template inline void output(Head&& head, Tail&&... tail) { cout << head; if (sizeof...(tail)) cout << " "; output(forward(tail)...); } template ::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 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 inline vector makeVector(const T &init_value, size_t sz) { return vector(sz, init_value); } template inline auto makeVector(const T &init_value, size_t sz, Args... args) { return vector(init_value, args...))>(sz, makeVector(init_value, args...)); } template class FixPoint : Func { public: explicit constexpr FixPoint(Func&& f) noexcept : Func(forward(f)) {} template constexpr decltype(auto) operator()(Args&&... args) const { return Func::operator()(*this, std::forward(args)...); } }; template static inline constexpr decltype(auto) makeFixPoint(Func&& f) noexcept { return FixPoint{forward(f)}; } template struct reverse_t { Container &c; reverse_t(Container &c) : c(c) {} auto begin() { return c.rbegin(); } auto end() { return c.rend(); } }; template auto reversed(Container &c) { return reverse_t(c); } template inline bool chmax(T &a, const T &b) noexcept { return b > a && (a = b, true); } template inline bool chmin(T &a, const T &b) noexcept { return b < a && (a = b, true); } template inline T diff(const T &a, const T &b) noexcept { return a < b ? b - a : a - b; } void operator|=(vector::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 struct FenwickTree { vector 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 ss(N + 1); repc(i, 1, N) input(ss[i]); FenwickTree 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); if (X - ss[i] / 2 + S == X) { return output(S), 0; } } return 0; }