#include <bits/stdc++.h>
using namespace std;
string S;
int mindist(char a, char b) {
  int x = (char)a - 'a';
  int y = (char)b - 'a';
  if (x > y) {
    swap(x, y);
  }
  int ans1 = 0;
  for (int j = x; j < y; ++j) {
    ++ans1;
  }
  int ans2 = 0;
  int j = y;
  while (j != x) {
    ++ans2;
    ++j;
    j %= 26;
  }
  return min(ans1, ans2);
}
bool ispal(string S) {
  return 0;
  string T = S;
  reverse(T.begin(), T.end());
  return S == T;
}
int main() {
  int N, K;
  cin >> N >> K;
  --K;
  cin >> S;
  K = min(K, N - K - 1);
  int Mid = N / 2;
  if (N % 2 == 0) {
    --Mid;
  }
  int Ans = mindist(S[K], S[N - K - 1]);
  S[K] = S[N - K - 1];
  int Start = 0;
  int End = Mid;
  while (Start < K) {
    if (S[Start] != S[N - Start - 1]) {
      break;
    }
    Start++;
  }
  while (End > K) {
    if (S[End] != S[N - End - 1]) {
      break;
    }
    --End;
  }
  if (End - K >= K - Start) {
    int k = K - 1;
    int tans = 0;
    bool f = false;
    while (k >= Start) {
      Ans += mindist(S[k], S[N - k - 1]);
      if (S[k] != S[N - k - 1]) {
        f = true;
      }
      S[k] = S[N - k - 1];
      if (k != Start) {
        ++tans;
      }
      --k;
    }
    if (f) {
      k = Start;
      Ans += tans;
      ++Ans;
    } else {
      k = K;
    }
    f = false;
    tans = 0;
    for (; k <= End; ++k) {
      Ans += mindist(S[k], S[N - k - 1]);
      if (S[k] != S[N - k - 1]) {
        f = true;
      }
      S[k] = S[N - k - 1];
      if (k != End) {
        tans++;
      }
    }
    if (f) {
      Ans += tans;
    }
  } else {
    int k = K + 1;
    bool f = false;
    int tans = 0;
    while (k <= End) {
      Ans += mindist(S[k], S[N - k - 1]);
      if (S[k] != S[N - k - 1]) {
        f = true;
      }
      S[k] = S[N - k - 1];
      if (k != End) {
        tans++;
      }
      ++k;
    }
    if (f) {
      Ans += tans;
      ++Ans;
      k = End;
    } else {
      k = K;
    }
    f = false;
    tans = 0;
    for (; k >= 0; --k) {
      Ans += mindist(S[k], S[N - k - 1]);
      if (S[k] != S[N - k - 1]) {
        f = true;
      }
      S[k] = S[N - k - 1];
      if (k != Start) {
        tans++;
      }
    }
    if (f) {
      Ans += tans;
    }
  }
  cout << Ans << endl;
  return 0;
}
