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

ll floor_sqrt(ll N){
  assert(N >= 0);
  ll ok = 0;
  ll ng = N + 1;
  while(abs(ok - ng) > 1){
    ll mid = (ok + ng) / 2;
    (mid <= N / mid ? ok : ng) = mid;
  }
  return ok;
}

ll isqrt(ll n){
  ll x = n;
  ll y = (x + 1) / 2;
  while(y < x){
    x = y;
    y = (x + n / x) / 2;
  }
  return x;
}

int main(){
  ll N;cin >> N;
  cout << isqrt(N) << '\n';
}