#include <stdio.h>
int main()
{
double solut(double,double,double,double );//函数原型声明
double a,b,c,d;
scanf("%lf%lf%lf%lf",&a,&b,&c,&d);
printf("%.2f",solut(a,b,c,d));
system("pause");
return 0;
}
double solut(double a,double b,double c,double d)
{
double x=1,x0;
do
{
x0=x;
x=x0-(a*x*x*x+b*x*x+c*x+d)/(3*a*x*x+2*b*x+c);
}
while(fabs(x-x0)>=1e-10);
return x;
}