백준 1789

package baekjoon.그리디;

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

class Main1789 {

   public static void main(String[] args) throws Exception {
      BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
      long S = Long.parseLong(br.readLine());
      long i = 0;
      for (; i <= S; i++) {
         if (((i * i) + i) / 2 == S) {
            System.out.println(i);
            break;
         }
         if (((i * i) + i) / 2 > S) {
            System.out.println(i - 1);
            break;
         }
      }

   }
}