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

#define FOR(i,l,r) for(int i = (int) (l);i < (int) (r);i++)
template<typename T> bool chmax(T& a,const T& b){ return a < b ? (a = b,true) : false; }
template<typename T> bool chmin(T& a,const T& b){ return b < a ? (a = b,true) : false; }
typedef long long ll;

ll N;

int main()
{
	while(scanf("%lld",&N),N != -1){
		double lo = 0.0,hi = 1e18,mid;
		FOR(i,0,200){
			mid = (lo + hi) / 2.0;
			if(mid * mid * mid <= N){
				lo = mid;
			}
			else{
				hi = mid;
			}
		}
		printf("%.10f\n",lo);
	}

	return 0;
}