#include <bits/stdc++.h>
using namespace std;
int num(char c) {
  int ans = c - 96;
  return ans;
}
char ch[200000];
int ara[200000], bra[200000];
int n, p;
int prework() {
  int i, len = (n + 1) / 2, sum = 0;
  for (i = 1; i <= len; i++) {
    int diff = abs(ara[i] - ara[n - i + 1]);
    diff = min(diff, 26 - diff);
    bra[i] = diff;
    sum += diff;
  }
  p = min(p, abs(n + 1 - p));
  int ind1 = -1, ind2 = -1;
  for (i = p + 1; i <= len; i++) {
    if (bra[i]) ind1 = i;
  }
  for (i = p - 1; i > 0; i--) {
    if (bra[i]) ind2 = i;
  }
  if (ind1 != -1 && ind2 == -1) {
    sum += (ind1 - p);
  } else if (ind2 != -1 && ind1 == -1) {
    sum += (p - ind2);
  } else if (ind1 != -1 && ind2 != -1) {
    int a = abs(p - ind1);
    int b = abs(p - ind2);
    sum += (min(a, b) + a + b);
  }
  return sum;
}
int main() {
  int i;
  while (scanf("%d %d", &n, &p) != EOF) {
    scanf("%s", ch);
    for (i = 0; i < n; i++) {
      ara[i + 1] = num(ch[i]);
    }
    int ans = prework();
    printf("%d", ans);
    printf("\n");
  }
  return 0;
}
