#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, k, arr[102], s = 0;
  cin >> n >> k;
  for (int i = 0; i < n; i++) {
    cin >> arr[i];
    s += arr[i];
  }
  int c = 0;
  while (((float)s / n) < k - 0.5) {
    s += k;
    c++;
    n++;
  }
  cout << c << endl;
  return 0;
}
