#include <bits/stdc++.h>
using namespace std;
int main() {
  long n;
  cin >> n;
  long sum = 2;
  int k = 1;
  int b = 0;
  for (int i = 1;; i = i + k) {
    if (i == n) {
      break;
    }
    b++;
    if (b == 2) {
      b = b % 2;
      k++;
    }
    if (i > n) {
      break;
    }
    sum++;
  }
  cout << sum;
  return 0;
}
