#include <bits/stdc++.h>
using namespace std;
int main() {
  double n = {};
  double k = {};
  double value = {};
  double sum = 0;
  cin >> n >> k;
  std::vector<double> a;
  for (double i = 0; i < n; i++) {
    cin >> value;
    a.push_back(value);
    sum += value;
  }
  while (round(sum / a.size()) < k) {
    a.push_back(k);
    sum += k;
  }
  cout << a.size() - n;
  return 0;
}
