#include <bits/stdc++.h>
using namespace std;
int main() {
  double n, k, x, avg, avg2;
  int c = 0;
  int d = 1;
  cin >> n >> k;
  vector<double> marks(n);
  for (int i = 0; i < marks.size(); i++) {
    cin >> x;
    marks[i] = x;
  }
  avg = accumulate(marks.begin(), marks.end(), 0.0) / (n);
  avg2 = avg;
  while (int(avg2 + .5) != k) {
    avg2 = (avg * n + d * k) / (n + d);
    c = c + 1;
    d = d + 1;
  }
  cout << c;
  return 0;
}
