#include<stdio.h>
#include<math.h>
int main() {
    float a, b, c, d,e;
    scanf("%f %f %f", &a, &b, &c);
    d = (a + b + c) / 2;
    e= sqrt(s * (s - a) * (s - b) * (s - c));
    printf("%.2f\n", area);
}