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

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