>>207
#include<stdio.h>

double f(double x)
{
return 4/(1+x*x);
}

double f_integral(double a, double b, long n)
{
double h, ai;
double ret=0.0;
long i;

h=(b-a)/n;
for(i=0;i<=n;i++)
{
ai=a+i*h;
ret+=f(ai);
}
ret-=(f(a)+f(b))/2;
ret*=h;

return ret;
}

int main(void)
{
printf("%f\n", f_integral(0, 1, 1000));
return 0;
}