#include <iostream>
#include <cstdlib>
#include <time.h>

using namespace std;

double MAX = 20;

double f(double x)
{
    return x;
}

double randomPoint(double a, double b) {
    return a + (double)rand()/(double)(RAND_MAX+1) * (b-a);
}

double integerMC(int a, int b, int P) {
    int counter = 0;
    double random_x;
    double random_y;
    for(int i = 0; i < P; i++)
    {
        random_x = randomPoint(a, b);
        random_y = randomPoint(0, MAX);
        if(random_y <= f(random_x)) counter++;
    }
    return counter/(double)P * (b-a) * MAX;
}

int main() {
    srand(time(NULL));
    double pole = integerMC(0, MAX, 10000);
    cout << pole;
    return 0;
}