capdoi.cpp

#include<iostream>
#include<cstdlib>
#include<vector>
#include<unordered_map>

#define long long long
#define nln '\n'

using namespace std;

int main()
{
    cin.tie(0)->sync_with_stdio(0);
    cout.tie(0)->sync_with_stdio(0);
    //freopen("capdoi.inp", "r", stdin);
    long n, x;
    cin >> n >> x;
    unordered_map<long, long> sum;
    long ans = 0;
    while (n--){
        long y;
        cin >> y;
        ans += sum[x-y];
        ++sum[y];}
    cout << ans << nln;
    return 0;
}