#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, pos;
  long long int ans = 0;
  cin >> n >> pos;
  string s;
  cin >> s;
  if (n % 2 == 0) {
    int exr = pos, exl = pos, flag = 0, start, en;
    if (pos <= n / 2) {
      start = 0;
      en = n / 2;
    } else {
      start = n / 2;
      en = n;
    }
    for (int i = start; i < en; i++) {
      if (s[i] != s[n - i - 1]) {
        if ((int)s[i] - 97 < (int)s[n - i - 1] - 97) {
          char temp = s[i];
          s[i] = s[n - i - 1];
          s[n - i - 1] = temp;
        }
        int g = ((int)s[i] - 97) - ((int)s[n - i - 1] - 97);
        int h = (((int)s[n - i - 1] - 97) - ((int)'a' - 97)) +
                (((int)'z' - 97) - ((int)s[i] - 97)) + 1;
        ans += min(g, h);
        exr = i;
        if (flag == 0) {
          exl = i;
          flag = 1;
        }
      }
    }
    pos--;
    if (pos - exl <= exr - pos) {
      int prevpos = pos;
      for (int i = pos - 1; i >= exl; i--) {
        if (s[i] != s[n - i - 1]) {
          ans += prevpos - i;
          prevpos = i;
        }
      }
      for (int i = pos + 1; i <= exr; i++) {
        if (s[i] != s[n - i - 1]) {
          ans += i - prevpos;
          prevpos = i;
        }
      }
      cout << ans << endl;
    } else {
      int prevpos = pos;
      for (int i = pos + 1; i <= exr; i++) {
        if (s[i] != s[n - i - 1]) {
          ans += i - prevpos;
          prevpos = i;
        }
      }
      for (int i = pos - 1; i >= exl; i--) {
        if (s[i] != s[n - i - 1]) {
          ans += prevpos - i;
          prevpos = i;
        }
      }
      cout << ans << endl;
    }
  } else {
    int exr = pos, exl = pos, flag = 0, start, en;
    if (pos <= (n - 1) / 2) {
      start = 0;
      en = (n - 1) / 2;
    } else if (pos == (n + 1) / 2) {
      start = 0;
      en = n;
    } else {
      start = (n + 1) / 2;
      en = n;
    }
    for (int i = start; i < en; i++) {
      if (s[i] != s[n - i - 1]) {
        if ((int)s[i] - 97 < (int)s[n - i - 1] - 97) {
          char temp = s[i];
          s[i] = s[n - i - 1];
          s[n - i - 1] = temp;
        }
        int g = ((int)s[i] - 97) - ((int)s[n - i - 1] - 97);
        int h = (((int)s[n - i - 1] - 97) - ((int)'a' - 97)) +
                (((int)'z' - 97) - ((int)s[i] - 97)) + 1;
        ans += min(g, h);
        exr = i;
        if (flag == 0) {
          exl = i;
          flag = 1;
        }
      }
    }
    pos--;
    if (pos - exl <= exr - pos) {
      int prevpos = pos;
      for (int i = pos - 1; i >= exl; i--) {
        if (s[i] != s[n - i - 1]) {
          ans += prevpos - i;
          prevpos = i;
        }
      }
      for (int i = pos + 1; i <= exr; i++) {
        if (s[i] != s[n - i - 1]) {
          ans += i - prevpos;
          prevpos = i;
        }
      }
      cout << ans << endl;
    } else {
      int prevpos = pos;
      for (int i = pos + 1; i <= exr; i++) {
        if (s[i] != s[n - i - 1]) {
          ans += i - prevpos;
          prevpos = i;
        }
      }
      for (int i = pos - 1; i >= exl; i--) {
        if (s[i] != s[n - i - 1]) {
          ans += prevpos - i;
          prevpos = i;
        }
      }
      cout << ans << endl;
    }
  }
  return 0;
}
