#include<iostream>
using namespace std;
int main(){
  long long N;
  cin>>N;
  if(N<1||N>1000000000){
      int x=1/0;
      cout<<x<<endl;
  }
  int answer=0;
  for(long long i=0;i<=100000;i++){
    if(i*(i+1)/2>=N){
      answer=i;
      break;
    }
  }
  cout<<answer<<endl;
}