Problem:
Score : 600 points

Problem Statement

You are given an integer sequence of length N, a = {a_1, a_2, …, a_N}, and an integer K.

a has N(N+1)/2 non-empty contiguous subsequences, {a_l, a_{l+1}, …, a_r} (1 ≤ l ≤ r ≤ N). Among them, how many have an arithmetic mean that is greater than or equal to K?

Constraints

All input values are integers.

1 ≤ N ≤ 2 \times 10^5

1 ≤ K ≤ 10^9

1 ≤ a_i ≤ 10^9

Input

Input is given from Standard Input in the following format:

N K
a_1
a_2
:
a_N

Output

Print the number of the non-empty contiguous subsequences with an arithmetic mean that is greater than or equal to K.

Sample Input 1

3 6
7
5
7

Sample Output 1

5

All the non-empty contiguous subsequences of a are listed below:

{a_1} = {7}

{a_1, a_2} = {7, 5}

{a_1, a_2, a_3} = {7, 5, 7}

{a_2} = {5}

{a_2, a_3} = {5, 7}

{a_3} = {7}

Their means are 7, 6, 19/3, 5, 6 and 7, respectively, and five among them are 6 or greater. Note that {a_1} and {a_3} are indistinguishable by the values of their elements, but we count them individually.

Sample Input 2

1 2
1

Sample Output 2

0

Sample Input 3

7 26
10
20
30
40
30
20
10

Sample Output 3

13

Solution in C++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <bits/stdc++.h>
using namespace std;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

#define COUT(x) cout << #x << " = " << (x) << " (L" << __LINE__ << ")" << endl
template<class T1, class T2> ostream& operator << (ostream &s, pair<T1,T2> P)
{ return s << '<' << P.first << ", " << P.second << '>'; }
template<class T> ostream& operator << (ostream &s, vector<T> P)
{ for (int i = 0; i < P.size(); ++i) { if (i > 0) { s << " "; } s << P[i]; } return s; }
template<class T> ostream& operator << (ostream &s, vector<vector<T> > P)
{ for (int i = 0; i < P.size(); ++i) { s << endl << P[i]; } return s << endl; }
template<class T> ostream& operator << (ostream &s, set<T> P)
{ for(auto it : P) { s << "<" << it << "> "; } return s << endl; }
template<class T1, class T2> ostream& operator << (ostream &s, map<T1,T2> P)
{ for(auto it : P) { s << "<" << it.first << "->" << it.second << "> "; } return s << endl; }



template <class Abel> struct BIT {
    const Abel UNITY_SUM = 0;                       // to be set
    vector<Abel> dat;
    
    /* [1, n] */
    BIT(int n) : dat(n + 1, UNITY_SUM) { }
    void init(int n) { dat.assign(n + 1, UNITY_SUM); }
    
    /* a is 1-indexed */
    inline void add(int a, Abel x) {
        for (int i = a; i < (int)dat.size(); i += i & -i)
            dat[i] = dat[i] + x;
    }
    
    /* [1, a], a is 1-indexed */
    inline Abel sum(int a) {
        Abel res = UNITY_SUM;
        for (int i = a; i > 0; i -= i & -i)
            res = res + dat[i];
        return res;
    }
    
    /* [a, b), a and b are 1-indexed */
    inline Abel sum(int a, int b) {
        return sum(b - 1) - sum(a - 1);
    }
    
    /* debug */
    void print() {
        for (int i = 1; i < (int)dat.size(); ++i) cout << sum(i, i + 1) << ",";
        cout << endl;
    }
};

int main() {
    int N;
    long long K;
    cin >> N >> K;
    vector<long long> S(N+1, 0);
    for (int i = 0; i < N; ++i) {
        long long a;
        cin >> a;
        S[i+1] = S[i] + (a - K);
    }
    vector<long long> SS = S;
    sort(SS.begin(), SS.end());
    SS.erase(unique(SS.begin(), SS.end()), SS.end());
    long long res = 0;
    BIT<long long> bit(N+10);
    for (int i = 0; i <= N; ++i) {
        int id = lower_bound(SS.begin(), SS.end(), S[i]) - SS.begin();
        res += bit.sum(id+1);
        bit.add(id+1, 1);

        //cout << S[i] << ": " << id << endl; bit.print();
    }
    cout << res << endl;
}