#include <bits/stdc++.h>
int main() {
  int N, C, K;
  scanf("%d", &N);
  double Number[N], Sum = 0.0;
  scanf("%d", &K);
  for (C = 0; C < N; C++) {
    scanf("%lf", &Number[C]);
    Sum += Number[C];
  }
  C = 0;
  while (round(Sum / (N + C)) < K) {
    Sum += K;
    C++;
  }
  printf("%d\n", C);
  return 0;
}
