#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, i;
	double x, r1, r2, d;

	for (N=1 ; fabs(a - ANS) >= 0.001; N++ ) {
		d = 1.0 / (double)N;
		r1 = f(0.0);
		a = 0.0;
		for (i=1, x=d; i<=N; i++, x+=d) {
			r2 = f(x);
			a += ((r1 + r2) * d) / 2.0;
			r1 = r2;
		}
	}
	printf("%f\n", a);
	return 0;
}