#include <bits/stdc++.h>
#pragma comment(linker, "/STACK:102400000,102400000")
using namespace std;
int n, k;
int a[139];
bool judge(long long x) {
  double sum = 0;
  for (int i = (1); i < n + 1; i++) sum += a[i];
  for (int i = (1); i < x + 1; i++) sum += k;
  return sum / (n + x) * 10 >= (k - 0.5) * 10;
}
long long Bsearch(long long l, long long r) {
  while (l < r) {
    long long mid = (l + r) >> 1;
    if (judge(mid))
      r = mid;
    else
      l = mid + 1;
  }
  return l;
}
int main() {
  scanf("%d%d", &n, &k);
  for (int i = (1); i < n + 1; i++) scanf("%d", &a[i]);
  printf("%d\n", Bsearch(0, 100000));
  return 0;
}
