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

#define pi 3.14159265
//function for area
float area(float base,float height)
{
    return 0.5*base*height;
}


int main()
{
    float height,angle1,angle2,base,Area;
    scanf("%f%f%f",&height,&angle1,&angle2);

    base=(tan(angle1*pi/180)+tan(angle2*pi/180))*height;

    Area= area(base,height);
    printf("%.6f\n",Area);

    return 0;
}