function processData(input) {
    //Enter your code here
    var ip = input.split(/\s+/g);
    var lenArr = ip.length;
    var strLen = ip[1].length;
    var i = 1;

    while(i<lenArr)
        {
 
            convertToAscii(ip[i]);
            i++;
        }

    
} 
function convertToAscii(str)
{
 
    var cstrLen = str.length;
    var i = 0;
    var j = 0;
    var ascArr = new Array();
    var receivedCounter = 0;
    for(i=0;i<cstrLen;i++)
        {
            ascArr[j] = str[i].charCodeAt();
            j++;
        }
  
   findPalindrome(ascArr);//97,98,99,100
}

function findPalindrome(asciiArray)
{
    var asciiArrayLen = asciiArray.length;
    var i = 0;
    var j = asciiArrayLen-1;
    var counter = 0;
   
    while(i<=j)
        {
   
            if(asciiArray[i]<asciiArray[j])
            {
                while(asciiArray[i]!=asciiArray[j])    
                    {
                        asciiArray[j] = asciiArray[j]-1;
                        counter++;
                    }
            }
            else
            {
                while(asciiArray[i]!=asciiArray[j])    
                    {
                        asciiArray[i] = asciiArray[i]-1;
                        counter++;
                    }
            }
            i++;
            j--;   
 
        }
    console.log(counter);
}

process.stdin.resume();
process.stdin.setEncoding("ascii");
_input = "";
process.stdin.on("data", function (input) {
    _input += input;
});

process.stdin.on("end", function () {
   processData(_input);
});