#include <stdio.h>
#include <math.h>
 
typedef struct {
    double a;
    double b;
    double c;
} Triangle;
 
double calculate_area(Triangle t) {
    double p = (t.a + t.b + t.c) / 2;
    return sqrt(p * (p - t.a) * (p - t.b) * (p - t.c));
}
 
int main() {
    Triangle t;
 
    scanf("%lf", &t.a);
    scanf("%lf", &t.b);
    scanf("%lf", &t.c);
 
    double area = calculate_area(t);
 
    printf(" a : %.lf\n b : %.lf\n c : %.lf\n", t.a, t.b, t.c);
    printf("三角形の面積: %.6f\n", area);
 
    return 0;
}
 

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