https://school.programmers.co.kr/learn/courses/30/lessons/12985
function solution(n,a,b){
var answer = 0;
while( n>=2){
n/=2;//1.
answer++;//1.
a = Math.ceil(a/2);//2.
b = Math.ceil(b/2);//2.
if( a===b){//3.
return answer;//4.
}
}
}