#include <stdio.h>

int i;
int main()
{
	int ch = 1;
	double a, area;
switch(ch)
{
    case 1: printf("equilateral triangle \n");
            printf("value of side \n");
            scanf("%lf",&a);
           // printf("\n %f", a);
            area= 0.433*a*a;
            printf("\n %lf", area);
            break;

    default : break;

}
}