#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 11;
char ss[N];
int n, p;
int s1, s2;
int main() {
  while (scanf("%d %d", &n, &p) == 2) {
    --p;
    scanf("%s", ss);
    int i, j;
    s1 = 0, s2 = 0;
    int last;
    for (i = 0, j = n - 1, last = p; i < j; ++i, --j) {
      if (ss[i] != ss[j]) {
        int dis1 = abs(i - last), dis2 = abs(j - last);
        s1 += min(abs(ss[i] - ss[j]), 26 - abs(ss[i] - ss[j]));
        if (dis1 < dis2) {
          s1 += dis1;
          last = i;
        } else {
          s1 += dis2;
          last = j;
        }
      }
    }
    for (--i, ++j, last = p; i >= 0; --i, ++j) {
      if (ss[i] != ss[j]) {
        int dis1 = abs(i - last), dis2 = abs(j - last);
        s2 += min(abs(ss[i] - ss[j]), 26 - abs(ss[i] - ss[j]));
        if (dis1 < dis2) {
          s2 += dis1;
          last = i;
        } else {
          s2 += dis2;
          last = j;
        }
      }
    }
    printf("%d\n", min(s1, s2));
  }
}
