https://www.acmicpc.net/problem/2417
Math.ceil 함수 사용하는 바람에 오히려 헤맸네
시간복잡도 O(log n)
import java.io.*;
import java.util.*;
public class Main
{
public static void main(String[] args)throws IOException
{
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
long n = Long.parseLong(br.readLine());
double temp = Math.sqrt(n);
long ans = (long)(temp);
if((ans*ans) < n)
ans++;
System.out.println(ans);
}
}