#include<iostream>
using namespace std;
int main(){
  long long N;
  cin >> N;
  long long ok = 0,ng = 100000;
  while(ng-ok > 1){
    long long mid = (ok+ng)/2;
    if(mid*(mid+1)/2 >= N){
      ng = mid;
    }
    else{
      ok = mid;
    }
  }
  cout << ng << endl;
}