#include <stdio.h>
#include <math.h>
 
int main(void) {
    double a, b, c;  // 三角形の3辺
    double s, area;  // 半周長と面積
 
    // 3辺の長さを入力
    printf("a:%d",a);
    scanf("%lf", &a);
    printf("b:%d",b);
    scanf("%lf", &b);
    printf("c:%d",c);
    scanf("%lf", &c);
 
    // 半周長を計算
    s = (a + b + c) / 2;
 
    // ヘロンの公式で面積を計算
    area = sqrt(s * (s - a) * (s - b) * (s - c));
 
    // 結果を出力
    printf("三角形の面積: %.6lf\n", area);
 
    return 0;
}

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