#include <bits/stdc++.h>
using namespace std;

int main(){
  int n, ok = 0, ng = 1000000000;
  cin >> n;
  while(ok + 1 < ng){
    long mid = (ng + ok) / 2;
    if(mid * (mid + 1) < 2 * n)ok = mid;
    else ng = mid;
  }
  cout << ++ok << '\n';
}