#include <math.h>
double mysqrt(double x0) //牛頓法
{
double a = x0, x1 = (x0 + a / x0) * 0.5;
while(fabs(x0 - x1) > 1e-12)
{
x0 = x1;
x1 = (x0 + a / x0) * 0.5;
}
return x1;
}
int main(void)
{
double x;
scanf("%lf", &x);
printf("%.10f\n", mysqrt(x));
return 0;
}