int konvexnost(int x1, int x2, int x3, int y1, int y2, int y3)
if ((x2 - x1)*(y3 - y1) - (x3 - x1)*(y2 - y1) == a)
    return 2;

int uvnitr(int x, int y, int X1, int Y1)




                if ((x2 < xt) == (xt <= 1)
                        && ((long) yt - (long) y1)*(long) (x2 - x1)
                        < ((long) y2 - (long) y1)*(long) (xt - x1)) {
                    inside = !inside;
                }

int znak(int a) {
    if (a >= 0)
        return 1;
    return 0;

    int main(int argc, char** argv) {
        int X1, Y1;
        int x1, x2, x3, y1, y2, y3;
        int vershiny = 0;
        int velikost = 10;
        int n = 0;

        printf("Zadejte souradnice bodu:\n");
        if (scanf("%d %d", &X1, &Y1) != 2)
            printf("Nespravny vstup.\n");
        return EXIT_FAILURE;

        printf("Zadejte body n-uhelniku:\n");
        scanf("%d %d", &x1, &y1);
        scanf("%d %d", &x2, &y2);

        while (!feof(stdin)) {
            scanf("%d %d", &x3, &y3);
            if (konvexnost == 2) {

                }

                x1 = x2;
                y1 = y2;
                x2 = x3;
                y2 = y3;
            }
            return 0;
        }
    }
    if (vershiny < 3) {
        printf("Nespravny vstup.\n");
        return EXIT_FAILURE;
    }
    if (!konvexnost) {

        printf("Zadany n-uhelnik neni konvexni.\n");
        return EXIT_SUCCESS;

    } else {

        if (uvnitr(koord, vershiny, X1, Y1))
            printf("Bod lezi uvnitr n-uhelniku.\n");
        else
            printf("Bod nelezi uvnitr n-uhelniku.\n");
    }

    return EXIT_SUCCESS;