#include <bits/stdc++.h>
using namespace std;
int main() {
  int sum = 0, pos = 0;
  string s;
  cin >> s;
  for (int i = 0; i < s.length(); i++)
    sum += min(abs(pos - (s[i] - 'a')), 26 - abs(pos - (s[i] - 'a'))),
        pos = s[i] - 'a';
  cout << sum;
  return 0;
}
