#include <bits/stdc++.h>
using namespace std;
const int INF = 1e9;
const int MOD = 1e9 + 7;
int n, p;
char s[100001], ss[100001];
int main() {
  scanf("%d %d", &n, &p);
  p--;
  scanf("%s", &s);
  bool ok = 1;
  for (int(i) = 0; (i) < (n); (i)++) {
    if (s[i] != s[n - i - 1]) ok = 0;
  }
  if (ok) return 0 * puts("0");
  int cnt1 = 0;
  {
    for (int(i) = 0; (i) < (n); (i)++) ss[i] = s[i];
    bool pass = 0;
    for (int where = p, step = 0; !(where == p && pass);
         where = (where + 1) % n, step++) {
      if (ss[where] != ss[n - where - 1]) {
        int up = 0, down = 0;
        for (int cur = ss[where] - 'a'; cur != ss[n - where - 1] - 'a';
             cur = (cur + 1) % 26)
          up++;
        for (int cur = ss[where] - 'a'; cur != ss[n - where - 1] - 'a';
             cur = (cur - 1 + 26) % 26)
          down++;
        cnt1 += step;
        cnt1 += min(up, down);
        ss[where] = ss[n - where - 1];
        step = 0;
      }
      pass = 1;
    }
  }
  int cnt2 = 0;
  {
    for (int(i) = 0; (i) < (n); (i)++) ss[i] = s[i];
    bool pass = 0;
    for (int where = p, step = 0; !(where == p && pass);
         where = (where - 1 + n) % n, step++) {
      if (ss[where] != ss[n - where - 1]) {
        int up = 0, down = 0;
        for (int cur = ss[where] - 'a'; cur != ss[n - where - 1] - 'a';
             cur = (cur + 1) % 26)
          up++;
        for (int cur = ss[where] - 'a'; cur != ss[n - where - 1] - 'a';
             cur = (cur - 1 + 26) % 26)
          down++;
        cnt2 += step;
        cnt2 += min(up, down);
        ss[where] = ss[n - where - 1];
        step = 0;
      }
      pass = 1;
    }
  }
  int cnt3 = 0;
  {
    for (int(i) = 0; (i) < (n); (i)++) ss[i] = s[i];
    int leftmost = INF, rightmost = -INF;
    for (int where = 0; where < n; where++) {
      if (ss[where] != ss[n - where - 1]) {
        int up = 0, down = 0;
        for (int cur = ss[where] - 'a'; cur != ss[n - where - 1] - 'a';
             cur = (cur + 1) % 26)
          up++;
        for (int cur = ss[where] - 'a'; cur != ss[n - where - 1] - 'a';
             cur = (cur - 1 + 26) % 26)
          down++;
        cnt3 += min(up, down);
        ss[where] = ss[n - where - 1];
        leftmost = min(leftmost, where);
        rightmost = max(rightmost, where);
      }
    }
    cnt3 += min(abs(p - leftmost) + rightmost - leftmost,
                abs(p - rightmost) + rightmost - leftmost);
  }
  int cnt4 = 0;
  {
    for (int(i) = 0; (i) < (n); (i)++) ss[i] = s[i];
    int leftmost = INF, rightmost = -INF;
    for (int where = n - 1; where >= 0; where--) {
      if (ss[where] != ss[n - where - 1]) {
        int up = 0, down = 0;
        for (int cur = ss[where] - 'a'; cur != ss[n - where - 1] - 'a';
             cur = (cur + 1) % 26)
          up++;
        for (int cur = ss[where] - 'a'; cur != ss[n - where - 1] - 'a';
             cur = (cur - 1 + 26) % 26)
          down++;
        cnt4 += min(up, down);
        ss[where] = ss[n - where - 1];
        leftmost = min(leftmost, where);
        rightmost = max(rightmost, where);
      }
    }
    cnt4 += min(abs(p - leftmost) + rightmost - leftmost,
                abs(p - rightmost) + rightmost - leftmost);
  }
  printf("%d\n", min(cnt1, min(cnt2, min(cnt3, cnt4))));
  return 0;
}
