#include <bits/stdc++.h>
int main() {
  double avg, sum = 0.0, tar;
  int n, k, a[100], i;
  scanf("%d %d", &n, &k);
  for (i = 0; i < n; i++) {
    scanf("%d", &a[i]);
  }
  for (i = 0; i < n; i++) {
    sum += a[i];
  }
  avg = sum / n;
  tar = k - 0.5;
  i = 0;
  while (avg < tar) {
    sum += k;
    i++;
    avg = sum / (n + i);
  }
  printf("%d", i);
  return 0;
}
