#include<iostream>
#include<algorithm>
#include<vector>
#include<queue>
#include<deque>
#include<map>
#include<set>
#include<string>
#include<sstream>
#include<cstdio>
#include<cmath>
#include<cstring>
#include<cctype>
#include<climits>
using namespace std;
#define REP(i, j) for(int i = 0; i < j; i++)
#define FOR(i, j, k) for(int i = j; i < k; i++)
#define P pair<int, int>
const int INF = INT_MAX / 2;

int main(){
    int q;
    while(cin >>q && q != -1){
        double bef = q / 2;
        double stp = sqrt(0.00001 * q);
        while(sqrt((bef * bef * bef) - q) > stp){
            bef = bef - ((bef * bef * bef - q) / (3 * bef * bef));
        }
        printf("%.6lf\n", bef);
    }
    return 0;
}