#include <bits/stdc++.h>
using namespace std;
int main() {
  int N, ans = 2, t = 1;
  cin >> N;
  --N;
  while (N > 0) {
    N -= t;
    ++ans;
    if (N <= 0) {
      break;
    }
    ++t;
    N -= t;
    ++ans;
  }
  cout << ans << endl;
  return 0;
}
