#include <stdio.h>
#define ABS(X) ((X)<0?-(X):(X))

int main(){
    int q;
    double x;
    
    while(scanf("%d",&q)){
        if (q==-1) break;
        for (x=q/2.0; ABS(x*x*x-q) >= 0.00001*q; x-=(x*x*x-q)/(3*x*x));
        printf("%f\n", x);
    }
    
    return 0;
}