#include <bits/stdc++.h>
using namespace std;
using ll=long long;
using ull=unsigned long long;
#define rep(i,n) for(int i=0; i<(n); i++)

int main(){
  ll N; cin>>N;
  ll l=0, r=80000;
  while(r-l>1){
    int m=(l+r)/2;
    if(m*(m+1)/2>=N) r=m; else l=m;
  }
  cout<<r<<"\n";
  return 0;
}