import std.stdio;
import std.algorithm;
import std.string;
import std.functional;
import std.array;
import std.conv;
import std.math;
import std.typecons;
import std.regex;
import std.range;

void main(){

    while(true){
	real n = readln().chomp().to!real;
	if(n==-1) break;
	real l,m,h;
	l = 0;
	h = n;
	m = (h+l)/2.0;
	while(abs(pow(m,3)-n) >= n*(1e-7)){
	    if( pow(m,3) < n){
		l = m;
	    }else{
		h = m;
	    }
	    m = (h+l)/2.0;
	}
	writef("%.7f\n",m);
    }

}