#include <bits/stdc++.h>
using namespace std;
char cad[100005];
bool prim[100005];
bool seg[100005];
vector<int> uno;
vector<int> dos;
int n;
int distancia(char i, char j) {
  char a = i;
  int cont = 0, mini = 50;
  while (a != j) {
    cont++;
    a++;
    if (a > 'z') a = 'a';
  }
  mini = min(cont, mini);
  a = i;
  cont = 0;
  while (a != j) {
    cont++;
    a--;
    if (a < 'a') a = 'z';
  }
  mini = min(cont, mini);
  return mini;
}
int simula1(int pos) {
  int cont = 0, mini = 1 << 30, save = pos;
  while (!prim[pos]) {
    pos++;
    cont++;
    if (pos == n) pos = 0;
  }
  mini =
      min(mini, cont + min(abs(uno[uno.size() - 1] - pos), abs(uno[0] - pos)));
  cont = 0;
  pos = save;
  while (!prim[pos]) {
    pos--;
    cont++;
    if (pos == -1) pos = n - 1;
  }
  mini =
      min(mini, cont + min(abs(uno[uno.size() - 1] - pos), abs(uno[0] - pos)));
  return mini;
}
int simula2(int pos) {
  int cont = 0, mini = 1 << 30, save = pos, l;
  while (!seg[pos]) {
    pos++;
    cont++;
    if (pos == n) pos = 0;
  }
  mini =
      min(mini, cont + min(abs(dos[dos.size() - 1] - pos), abs(dos[0] - pos)));
  cont = 0;
  pos = save;
  while (!seg[pos]) {
    pos--;
    cont++;
    if (pos == -1) pos = n - 1;
  }
  mini =
      min(mini, cont + min(abs(dos[dos.size() - 1] - pos), abs(dos[0] - pos)));
  return mini;
}
int main() {
  int p;
  scanf("%d %d", &n, &p);
  scanf("\n%s", cad);
  int i = 0, j = n - 1;
  int res = 0;
  while (i < j) {
    if (cad[i] == cad[j]) {
      i++;
      j--;
      continue;
    }
    prim[i] = true;
    uno.push_back(i);
    dos.push_back(j);
    seg[j] = true;
    res += distancia(cad[i], cad[j]);
    i++;
    j--;
  }
  if (res != 0) {
    int sum1 = 0, sum2 = 0;
    for (i = 0; i < dos.size() - 1; i++) sum2 += (dos[i] - dos[i + 1]);
    for (i = uno.size() - 1; i > 0; i--) sum1 += (uno[i] - uno[i - 1]);
    int aux = simula1(p - 1) + sum1;
    int aux2 = simula2(p - 1) + sum2;
    if (aux < aux2)
      res += aux;
    else
      res += aux2;
  }
  printf("%d\n", res);
  return 0;
}
