#include <algorithm>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <math.h>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <utility>
#include <vector>


using namespace std;


using ull = unsigned long long;
using ll = long long;
using ld = long double;


#define all(v) v.begin(), v.end()
#define rep(i, n) for (ll i = 0; i < n; ++i)
#define rep2(i, n, m) for (ll i = n; i <= m; ++i)
#define rep3(i, n, m) for (ll i = n; i >= m; --i)


template<class T> using pqg = priority_queue<T, vector<T>, greater<T>>;
template<class T> using pq  = priority_queue<T>;


template<class S, class T> inline bool chmax(S &a, T b) { if (a < b) { a = b; return true; } return false; }
template<class S, class T> inline bool chmin(S &a, T b) { if (a > b) { a = b; return true; } return false; }


int main() {
  int n;
  cin >> n;

  ll l = 0, r = n+1;
  while (r - l > 1) {
    ll m = (l + r) / 2;
    if (m * (m + 1) / 2 >= n) r = m;
    else l = m;
  }

  cout << r << endl;
  return 0;
}