import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.math.BigDecimal;
import java.math.BigInteger;
public class Main {
    public static void main(String[]args)throws Exception
    {
        BufferedReader in=new BufferedReader(new InputStreamReader(System.in)) ;
        String s=in.readLine();
        BigInteger b=new BigInteger(s),lo=new BigInteger("0"),hi,two=new BigInteger("2"),mid=BigInteger.ZERO,ans=BigInteger.ZERO;
        hi=b;
        while(hi.compareTo(lo)>0)
        {
           mid=(lo.add(hi)).divide(two);
           ans=mid.multiply(mid);
           if(ans.compareTo(b)==0)break;
           else if(ans.compareTo(b)<0)lo=mid.add(BigInteger.ONE);
           else hi=mid.subtract(BigInteger.ONE);
        }
        if(ans.compareTo(b)<=0);
        else mid=mid.subtract(BigInteger.ONE);
        BigDecimal mid1=BigDecimal.ZERO, lo1=new BigDecimal("0"),hi1=BigDecimal.ONE,two1=new BigDecimal("2"),ans1,mid2=new BigDecimal(mid),b1=new BigDecimal(b);
        for(int i=0;i<=150;i++)
        {
          mid1=(lo1.add(hi1)).divide(two1);
          ans1=mid1.multiply(mid1).add(mid2.multiply(mid2).add(two1.multiply(mid1.multiply(mid2))));
           if(ans1.compareTo(b1)==0)   break;
            else if(ans1.compareTo(b1)<0)lo1=mid1;
            else hi1=mid1;
        }
        mid2=mid2.add(mid1);
        mid2=mid2.setScale(12, BigDecimal.ROUND_HALF_UP);
        System.out.println(mid2);
 
    }
}

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