#include<stdio.h>
#include<math.h>
#define f(x) ((x)*(x)*exp(x))
#define exact_value 2.0*(exp(2)-1.0)

main()
{
   int i;
   float n,a,b,h,x1,x2,x3,ans,gosa;

     printf("N=");
     scanf("%f",&n);
     printf("[a,b]=");
     scanf("%f %f",&a,&b);
     ans=0.0;
     h=(b-a)/n;
     for(i=0;i<=n-2;i+=2){
       x1=a+i*h;
       x2=x1+h;
       x3=x1+2.0*h;
       ans=ans+h/3.0*(f(x1)+4.0*f(x2)+f(x3));
     }
     gosa=fabs(exact_value-ans);
     printf("N=   %f\n",n);
     printf(" [%f,%f]\n",a,b);
     printf("    %15.7e\n",ans);
     printf("exact    %15.7e\n",exact_value);
     printf("error    %15.7e\n",gosa);
   return(0);
}