#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int n;
  double k;
  cin >> n >> k;
  int temp = n;
  double marks[n];
  double sum = 0;
  for (int i = 0; i < n; i++) {
    cin >> marks[i];
    sum += marks[i];
  }
  double limit = k - 0.5;
  double avg = sum / n;
  while (avg < limit) {
    sum += k;
    n++;
    avg = sum / n;
  }
  cout << n - temp << endl;
  return 0;
}
