代码：

#include<bits/stdc++.h>
using namespace std;
double r1,r2;
int main()
{
	scanf("%lf%lf",&r1,&r2);
	printf("%.2lf\n",1.0/(1.0/r1+1.0/r2));
	return 0;
}

评测的时候出现了随机的re，还有显示远端 OJ 尚未返回编译信息。 https://www.luogu.com.cn/record/54284822 https://www.luogu.com.cn/record/54284885 https://www.luogu.com.cn/record/54285106 https://www.luogu.com.cn/record/54285348 https://www.luogu.com.cn/record/54285383 https://www.luogu.com.cn/record/54285769