#include<stdio.h>
#include<math.h>
double area(double a,double b,double c){
	double p = (a + b + c) * 0.5;
	double s = sqrt(p*(p-a) + p*(p-b) + p*(p-c));
	return s;
}
int main(){
	double a,b,c;
	scanf("%lf %lf %lf",&a,&b,&c);
	if(a + b > c && a+c > b && b + c > a){
		double s = area(a,b,c);
		printf("%.1lf",s);
	}
	else	return 0;
}

还是自己的编译器都是正确的数据放洛谷上就不行了