/* -*- coding: utf-8 -*-
 *
 * 1459.cc:  No.1459 スマホを落としたいだけなのに - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

/* typedef */

typedef long long ll;

/* global variables */

/* subroutines */

/* main */

int main() {
  int n;
  scanf("%d", &n);

  // a(a+1)/2>=n -> a^2+a-2n>=0
  // -> a>=(-1+sqrt(1+8n))/2

  int a0 = 0, a1 = (sqrt(1.0+(ll)n * 8) - 1) / 2 + 0.5;
  //printf("a0=%d, a1=%d\n", a0, a1);

  while (a0 + 1 < a1) {
    int a = (a0 + a1) / 2;
    if ((ll)a * (a + 1) / 2 >= n) a1 = a;
    else a0 = a;
  }

  printf("%d\n", a1);
  return 0;
}