#include <bits/stdc++.h>
using namespace std;
int n, i, m = 0, a[100];
float avg = 0, k;
int main() {
  cin >> n >> k;
  for (i = 0; i < n; i++) {
    cin >> a[i];
    avg += a[i];
  }
  while (round(avg / n) < k) {
    n++;
    avg += k;
    m++;
  }
  cout << m;
}
