#include <bits/stdc++.h>
const double eps = 1e-8;
const int oo = 0x3f3f3f3f;
using namespace std;
int n, k;
int a[111];
bool read() {
  if (!(cin >> n >> k)) return false;
  for (int i = 0; i < n; i++) {
    cin >> a[i];
  }
  return true;
}
void process() {
  double sum = 0;
  double avg = 0;
  for (int i = 0; i < n; i++) {
    sum += a[i];
  }
  avg = sum / n;
  int c = 0;
  while ((avg + 0.5) < k) {
    c++;
    n++;
    sum += k;
    avg = sum / n;
  }
  cout << c << endl;
}
int main() {
  int t = -1;
  while (t-- && read()) {
    process();
  }
  return 0;
}
