#include <bits/stdc++.h>
using namespace std;
int main() {
  string S;
  long long int answer = 0;
  cin >> S;
  for (long long int i = 0; i < 2 * pow(10, 5); i++) {
    if (i * (i + 1) / 2 >= 2 * pow(10, 5)) {
      answer = i;
      break;
    }
  }
  cout << answer << endl;
  return 0;
}
