#include <bits/stdc++.h>
int len;
int min(int a, int b) { return a > b ? b : a; }
int posdist(int a, int b) {
  if (a - b > 0)
    return min(a - b, len - a + b);
  else
    return min(b - a, len - b + a);
}
int dist(char a, char b) {
  if (a - b > 0)
    return min(a - b, 1 + 'z' - a + b - 'a');
  else
    return min(b - a, 1 + 'z' - b + a - 'a');
}
char a[1000000];
char b[1000000];
int main() {
  int i, count = 0, curr, xx, fl = 1;
  len = 5;
  scanf("%d%d", &len, &curr);
  scanf("%s", a);
  for (i = 0; i < len; i++) b[i] = a[i];
  curr--;
  xx = curr;
  for (i = curr;; i++) {
    if (i == xx) {
      if (fl == 0) break;
      fl = 0;
    }
    if (a[i] != a[len - 1 - i]) {
      count += min(posdist(curr, i), posdist(curr, len - 1 - i));
      count += dist(a[i], a[len - 1 - i]);
      a[i] = a[len - 1 - i];
      if (posdist(curr, i) > posdist(curr, len - 1 - i))
        curr = len - 1 - i;
      else
        curr = i;
    }
    if (i == len - 1) i = -1;
  }
  int count1 = 0;
  fl = 1;
  curr = xx;
  for (i = curr;; i--) {
    if (i == xx) {
      if (fl == 0) break;
      fl = 0;
    }
    if (b[i] != b[len - 1 - i]) {
      count1 += min(posdist(curr, i), posdist(curr, len - 1 - i));
      count1 += dist(b[i], b[len - 1 - i]);
      b[i] = b[len - 1 - i];
      if (posdist(curr, i) > posdist(curr, len - 1 - i))
        curr = len - 1 - i;
      else
        curr = i;
    }
    if (i == 0) i = len;
  }
  printf("%d\n", min(count, count1));
  return 0;
}
