#include<bits/stdc++.h>

using namespace std;
using ll = long long;
using pint = pair<int,int>;

#include <boost/multiprecision/cpp_int.hpp>
#include <boost/multiprecision/cpp_dec_float.hpp>
namespace mp = boost::multiprecision;
using Int = mp::cpp_int;                        // 任意長整数


int main()
{
	Int N;
   	string s(100000,'0');
  	s[0] = '1';
  	N = Int(s);
	Int n = sqrt(N);
	cout << n.str().size() << endl;
}