#include <stdio.h>
#include <math.h>

double f(double x)
{
	return pow(x, 3.0);
}

int main()
{
const double ANS = 1.0 / 4.0; 
double a = 0.0;
int N;

	for (N=1 ; fabs(a - ANS) >= 0.001; N++ ) {
		double x;
		double d = 1.0 / (double)N;
		for (x=0.0, a=0.0; x<=1.0; x+=d)
			a += ((d + d) * f(x)) / 2.0;
	}
	
	printf("%f\n", a);
	
	return 0;	
}