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

double f(double);
double integral(double (double), double, double, int);


double f(double t){
    return t;
}

int main(void){
    double r, a, b, c;
    int n;
    printf("Vvedite, pojaluista, a i b: ");
    if(scanf("%lf%lf", &a, &b)!=2)
    {
            printf("Cant't read");
            return -1;
    }
    printf("Esche vvedite, pojaluista, n: ");
    if(scanf("%d", &n)!=1)
    {
            printf("Cant't read");
            return -1;
    }
    if(n<0) return 0;
    while(n>0){
        r=integral(f,a,b,n);
//printf("%f %f\n",r,sgn);
        printf("Integral = %f\n",r);
        printf("Vvedite, pojaluista, a i b: ");
        if(scanf("%lf%lf", &a, &b)!=2)
        {
                printf("Cant't read");
                return -1;
        }
        printf("Esche vvedite, pojaluista, n: ");
        if(scanf("%d", &n)!=1)
        {
                printf("Cant't read");
                return -1;
        }
        if(n<0) return 0;
    }
    return 0;
}

double integral(double (*f)(double), double a, double b, int n){
    int i;
    double h, s=0, s1, s2;
    double A, B, fi=f(a), fi1, xi=a, xi1;
    h=(b-a)/(double)n;
//printf("%f %f %f",fi,xi,h);
    for(i=0; i<n-1; i++){
        xi1=a+(i+1)*h;
        fi1=f(xi1);
        A=(fi1-fi)/(xi1-xi);
        B=fi-(fi1-fi)*xi/(xi1-xi);
        s1=2*(pow(xi1,1.5)-pow(xi,1.5))/3;
        s2=2*(sign(xi1)*sqrt(fabs(xi1))-sign(xi)*sqrt(fabs(xi)));
        s+=(A*s1+B*s2);
        xi=xi1;
        fi=fi1;
    }
    return s;
}

int sign(double x){
    if(x<0) return -1;
    return 1;
}