#include <bits/stdc++.h>
using namespace std;
string s;
int a[123456];
int n, p;
int main() {
  cin >> n >> p;
  cin >> s;
  for (int i = 0; i < s.size(); i++) {
    int tmp1 = abs(s[i] - s[n - i - 1]);
    int tmp2;
    if (s[i] > s[n - i - 1])
      tmp2 = abs(s[i] - 26 - s[n - i - 1]);
    else
      tmp2 = abs(s[n - i - 1] - s[i] - 26);
    a[i + 1] = min(tmp1, tmp2);
  }
  int mid = (n + 1) / 2;
  int ans = 0x3f3f3f;
  if (p <= mid) {
    int ans1 = 0;
    int tmpp = p;
    for (int i = 1; i <= mid; i++)
      if (a[i]) {
        ans1 += a[i];
        ans1 += abs(tmpp - i);
        tmpp = i;
      }
    ans = min(ans1, ans);
    ans1 = 0;
    tmpp = p;
    for (int i = mid; i >= 1; i--)
      if (a[i]) {
        ans1 += a[i];
        ans1 += abs(tmpp - i);
        tmpp = i;
      }
    ans = min(ans1, ans);
  } else {
    int ans1 = 0;
    int tmpp = p;
    for (int i = mid + 1; i <= n; i++)
      if (a[i]) {
        ans1 += a[i];
        ans1 += abs(tmpp - i);
        tmpp = i;
      }
    ans = min(ans1, ans);
    ans1 = 0;
    tmpp = p;
    for (int i = n; i > mid; i--)
      if (a[i]) {
        ans1 += a[i];
        ans1 += abs(tmpp - i);
        tmpp = i;
      }
    ans = min(ans, ans1);
  }
  cout << ans << endl;
  return 0;
}
