import times, strutils, sequtils, math, algorithm, tables, sets, lists, intsets
import critbits, future, strformat, deques
template `max=`(x,y) = x = max(x,y)
template `min=`(x,y) = x = min(x,y)
template `mod=`(x,y) = x = x mod y
template scan2 = (scan(), scan())
template scan3 = (scan(), scan())
let read* = iterator: string {.closure.} =
    while true: (for s in stdin.readLine.split: yield s)
proc scan(): int = read().parseInt
proc scanf(): float = read().parseFloat
proc toInt(c:char): int =
    return int(c) - int('0')



proc solve():int=
  var
    n = scan()
    m = 1
  if n==1:
    return 1
  while (m+2)*(m-1)<=n*2:
    m+=1
  m-=1
  #echo m
  var sm = ((m+2)*(m-1) div (2))
  #echo (n-sm-1)+(m-1)
  return max(m,(n-sm)+(m-1))
  
  


  
echo solve()