[BOJ] 1789 수들의 합 (JAVA)

https://www.acmicpc.net/problem/1789

1789번: 수들의 합

import java.io.BufferedReader;
import java.io.InputStreamReader;

public class Main {
	
    public static void main(String[] args) throws Exception {

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        long S = Long.parseLong(br.readLine());
        long l = 1;
        long r = 100000;
        while (l < r) {
            long mid = (l + r) >> 1;
            long num = (mid * (mid + 1)) >> 1;
            if (S < num) r = mid;
            else l = mid + 1;
        }

        System.out.print(l - 1);

    }
	
}