function Main(input){
  const input = input.split(" ");
  var a = parseInt(input[0],10);
  var b = parseInt(input[1],10);
  var t = parseFloat(input[2],10)+0.5;
  var sum;
  
  while(b<t){
        sum += a;
        b = b+b;
}
  console.log(sum);
}
Main(require("fs").readFileSync("dev/stdin","utf8"));