#include<stdio.h>
#include<math.h>
 
float square(float a, float b, float c)
{
    float p = (a + b + c) / 2;
    float s = sqrt(p * (p - a) * (p - b) * (p - c));
    return s;
}
 
void main()
{
    float a, b, c;
    printf("%f",square(1,2,3));
    scanf("%f",&a);
}