#include <stdio.h>
#include <math.h>
int main()
{
    double a, b, c, p, S;
    p=(a+b+c)/2;
    S=sqrt(p*(p-a)*(p-b)*(p-c));
    scanf("%lf %lf %lf", &a, &b, &c);
    printf("%.1lf", S);
    return 0;
}
求助哪里出错，一直WA