#include <iostream>
#include <cmath>
#include <vector>
#include <algorithm>
using namespace std;
int main()
{
string s;
cin>>s;
int sum=0;
int temp='a';
for(int i=0;i<s.length();i++){
if((int)s[i]> temp){
    sum+=min(abs(temp-s[i]),temp+26-s[i]);
}else
sum+=min(temp-s[i],s[i]+26-temp);
temp=s[i];
}
cout<<sum<<endl;
    return 0;
}