#include <bits/stdc++.h>
using namespace std;
map<string, long> m;
int main() {
  long long t, i, n, j, x, y, res, k, count = 0, mi, ma;
  char a[100005];
  cin >> n >> k;
  mi = k;
  ma = k;
  cin >> a;
  for (i = 0; i < n / 2; i++) {
    if (a[i] != a[n - i - 1])
      count += min((long long)abs(a[i] - a[n - i - 1]),
                   (long long)26 - (long long)abs(a[i] - a[n - i - 1]));
  }
  if (k - 1 < n / 2) {
    for (i = 0; i < n / 2; i++) {
      if (a[i] != a[n - i - 1]) {
        mi = min(mi, i + 1);
        ma = max(ma, i + 1);
      }
    }
  } else {
    for (i = n / 2; i < n; i++) {
      if (a[i] != a[n - i - 1]) {
        mi = min(mi, i + 1);
        ma = max(ma, i + 1);
      }
    }
  }
  if (mi == k && ma == k)
    cout << count;
  else {
    res = min(k - mi, ma - k);
    if (res == (ma - k))
      count += 2 * (ma - k) + (k - mi);
    else
      count += 2 * (k - mi) + (ma - k);
    cout << count;
  }
  return 0;
}
