//also use arr.reverse
function processData(input) {
let string = input.split('\n');
let k = string[0].split(" ")[1];
let bill = string[1].split(" ").map(Number);
let b = string[2]
let res = 0
const total = bill.reduce((a, b)=>{
return a+b;
});
const discount = bill[k];
const refund = b - (total - discount) / 2;
if (refund != 0){
console.log(refund);
}else{
console.log("Bon Appetit");
}
}
process.stdin.resume();
process.stdin.setEncoding("ascii");
_input = "";
process.stdin.on("data", function (input) {
_input += input;
});
process.stdin.on("end", function () {
processData(_input);
});
