#include <stdio.h>
#include <math.h>
typedef struct{
double a;
double b;
double c;
}hen;
int main(void){
hen t;
double p,s;
scanf("%lf %lf %lf",&t.
a,&t.
b,&t.
c);
p=(t.a+t.b+t.c)/2;
s
=sqrt(p
*(p
-t.
a)*(p
-t.
b)*(p
-t.
c));
return 0;
}
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