#include <iostream>
#include <math.h>

using namespace std;

int main()
{
    double a = 2, b = 4, x, fx;
    int n = 10;
    double h = (b-a) / n;
    double x0,fx0;
    double xn, fxn;

    double wyn = 0;

    x0=a;
    fx0 = 0.5*(x0*x0);
    xn = a + n/n*(b-a);
    fxn = 0.5*(xn*xn);

    for (int i=1; i<=n-1; i++)
    {
        x = a + (i/n)*(b-a);
        fx = 0.5*(x*x);
        wyn = wyn + fx;
    }

    wyn = wyn + fx0/2 + fxn/2;

    wyn = wyn*h;

    cout << wyn << endl;
    system("pause");
    return 0;
}