>>662
include <stdio.h>
#include <math.h>

double f (double x) {return 4.0 / (1 + x*x);}

double integrateAux (double x, double h, double sum, int n) {
if (n <= 0) return sum;
else return integrate (x+2*h, h, sum + f (x) + 4 * f (x + h) + f (x + 2 * h), n-1);
}

double integrate (double x1, double x2, int n) {
double h;
h = (x2-x1)/n;

return integrateAux (x1, h, 0.0, n/2) * (x2-x1)/n / 3.0;
}

int main() {
printf("%lf\n", integrate(0.0, 1.0, 20));
return 0;
}