#include <bits/stdc++.h>
using namespace std;
const string maxS = "zzzzzzzzzzzzzzzzzzzzz";
const long long A = 100000000000000LL, N = 1000000;
char s[2];
string a;
long long i, j, n, m, d[N], _o[2], o, r, l, g;
int main() {
  cin >> n >> m;
  cin >> a;
  if (m >= n / 2) {
    m = n - m;
    for (i = 0; i < n / 2; i++) swap(a[i], a[n - i - 1]);
  } else
    m--;
  r = l = A;
  for (i = 0; i < n; i++) {
    s[0] = min(a[i], a[n - i - 1]);
    s[1] = max(a[i], a[n - i - 1]);
    d[i] = min((long long)(s[1] - s[0]),
               (long long)(s[0] - 'a') + (26 - (long long)(s[1] - 'a')));
  }
  for (i = m; i < n / 2; i++)
    if (d[i]) r = i;
  for (i = m; i >= 0; i--)
    if (d[i]) l = i;
  if (l == r && l == A) {
    cout << 0;
    return 0;
    ;
  }
  if (r == A) {
    o = d[m];
    for (i = l; i < m; i++) o += 1 + d[i];
    cout << o << "\n";
    return 0;
    ;
  }
  if (l == A) {
    o = d[m];
    for (i = m + 1; i <= r; i++) o += 1 + d[i];
    cout << o << "\n";
    return 0;
    ;
  }
  for (i = l; i <= r; i++) o += d[i];
  for (i = m + 1; i <= r; i++) _o[0] += 2, _o[1]++;
  for (i = l; i < m; i++) _o[0]++, _o[1] += 2;
  cout << o + min(_o[0], _o[1]);
}
