#include <bits/stdc++.h>
using namespace std;
float x[104], s, sum;
int tr(float s) {
  if (int(s * 10) % 10 >= 5) s = s + 1;
  s = int(s);
  return int(s);
}
int main() {
  float n, k;
  int v = 0;
  cin >> n >> k;
  for (int i = 0; i < n; i++) {
    cin >> x[i];
    s += x[i];
  }
  sum = s;
  s = s / n;
  while (tr(sum / (v + n)) < k) {
    sum += k;
    v++;
  }
  cout << v;
  return 0;
}
