function main(input){
  let list = input.split(" ");
  let n = parseInt(list[0]);//作る数
  let x = parseInt(list[1]);//一度に作れる数
  let t = parseInt(list[2]);//time
  let answer = (Math.floor(n/x)+1)*t;
  console.log(answer);
}
main(require("fs").readFileSync("/dev/stdin", "utf8"));