#include <stdio.h>
#include <math.h> 
 
struct Triangle {
    double a;
    double b;
    double c;
};
 
int main(void) {
    struct Triangle t;
    double s, area;
 
 
    scanf("%lf", &t.a);
    scanf("%lf", &t.b);
    scanf("%lf", &t.c);
 
 
    area = (t.a + t.b + t.c) / 2.0;
 
    s = sqrt(area * (area - t.a) * (area - t.b) * (area - t.c));
 
 
    printf("a : %g\n", t.a);
    printf("b : %g\n", t.b);
    printf("c : %g\n", t.c);
    printf("三角形の面積 : %f\n", s);
 
    return 0;
}

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