#include <bits/stdc++.h>
using namespace std;
int main() {
  int N, p;
  scanf("%d%d", &N, &p);
  int i;
  p--;
  string S;
  cin >> S;
  int sz = S.size(), add = 0, flag = 0, first, last;
  for (i = 0; i < sz / 2; i++) {
    char c1 = S[i], c2 = S[sz - 1 - i];
    if (c1 != c2) {
      if (flag == 0) {
        first = i;
        flag = 1;
      }
      last = i;
    }
    add += min(abs(c1 - c2), abs(26 - abs(c1 - c2)));
  }
  if (p > sz / 2) {
    p = sz - 1 - p;
  }
  if (flag == 0) {
    printf("0");
    return 0;
  }
  if (p != sz / 2) {
    if (last == first) {
      printf("%d", abs(p - last) + add);
      return 0;
    }
    if (last < p) {
      printf("%d", abs(p - first) + add);
      return 0;
    }
    if (first > p) {
      printf("%d", abs(p - last) + add);
      return 0;
    }
    printf(
        "%d",
        min(2 * (p - first) + (last - p), 2 * (last - p) + (p - first)) + add);
    return 0;
  }
  if (p == sz / 2) {
    if (sz % 2) {
      printf("%d", p - first + add);
      return 0;
    } else {
      p--;
      printf("%d", p - first + add);
      return 0;
    }
  }
}
