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

main()
{
    double s;
    double a, b;
    double x, dx;

    fprintf(stderr,"from ?\n");
    scanf("%lf", &a );

    fprintf(stderr,"to ?\n");
    scanf("%lf", &b );

    fprintf(stderr,"step ?\n");
    scanf("%lf", &dx );

    fprintf(stderr,"from %g to %g by step %g\n",a,b,dx);

    s=0.0;
    x=a;
    while( x<=b )
    {
	s = s + ( x * x ) * dx;
	x = x + dx;
    }
    printf("integral = %g\n", s );
}