#include <bits/stdc++.h>
using namespace std;

#define all(x) begin(x), end(x)
#ifdef CKISEKI
#define safe cerr << __PRETTY_FUNCTION__ << " line " << __LINE__ << " safe\n"
#define debug(a...) debug_(#a, a)
#define orange(a...) orange_(#a, a)
#include <experimental/iterator>
void debug_(auto s, auto ...a) {
  cerr << "\e[1;32m(" << s << ") = (";
  int f = 0;
  (..., (cerr << (f++ ? ", " : "") << a));
  cerr << ")\e[0m\n";
}
void orange_(auto s, auto L, auto R) {
  cerr << "\e[1;33m[ " << s << " ] = [ ";
  using namespace experimental;
  copy(L, R, make_ostream_joiner(cerr, ", "));
  cerr << " ]\e[0m\n";
}
#else
#define safe ((void)0)
#define debug(...) safe
#define orange(...) safe
#endif

using llf = long double;

int main() {
  cin.tie(nullptr)->sync_with_stdio(false);
  int s;
  cin >> s;

  auto valid = [s](llf r) {
    int64_t tot = 0;
    for (int i = -31622; i <= -1; ++i) {
      if (r * r < llf(i) * i)
        continue;
      llf l = sqrt(r * r - i * i);
      tot += floor(l);
    }
    return tot * 4 > s;
  };
  
  llf L = 0, R = 31622;  
  for (int iter = 0; iter < 60; ++iter) {
    llf M = (L + R) / 2;
    if (valid(M))
      R = M;
    else
      L = M;
  }
  cout << fixed << setprecision(15) << R << "\n";
  return 0;
}