#include <stdio.h>
#include <math.h>
 
typedef struct{
		double a;
		double b;
		double c;
}triangle;
 
int main(void){
 
	triangle length; 
 
	double k;
	double s;
 
	scanf("%lf %lf %lf",&length.a,&length.b,&length.c);
 
	k=(length.a+length.b+length.c)/2;
 
    s = sqrt(k*(k-length.a)*(k-length.b)*(k-length.c));
 
    printf("辺: a=%lf,b=%lf,c=%lf\n",length.a,length.b,length.c);
    printf("三角形の面積s = %lf", s);
 
    return 0;
}
 

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