#include <stdio.h>
#include <math.h>
int main(void) {
// your code goes here
double a,b;
double c,d,e;
scanf("%lf %lf %lf",&c
,&d
,&e
); b=(c+d+e)/2;
a
=sqrt(b
*(b
-c
)*(b
-d
)*(b
-e
)); return 0;
}
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