import sys
input = sys.stdin.readline
from collections import *

def f(x):
    if x==0:
        return 0
    
    res = 10**18
    
    for i in range(1, x+1):
        res = min(res, max(i, 1+f(x-i)))
    
    return res

N = int(input())
now = 0

for i in range(10**5):
    if N<=now+i:
        print(i)
        exit()
    
    now += i