function main(input){
    const args=input.split(' ');
    const n=args[0];
    const x=args[1];
    const t=args[2];
    let a=n/x;
    if(n%x!=0){
        a++;
    }
    console.log(a*t);
}

main(require('fs').readFileSync('/dev/stdin','utf8'));