就第一组数据是WA，后面都是AC

#include <iostream>
#include <cmath>
using namespace std;
double pyround(double num,int digit)//自定义pyround函数，可自定义位数
{
    double tmp1=num*pow(10,digit);
    double tmp2=round(tmp1);
    double res=tmp2*pow(0.1,digit);
    return res;
}

int main(){
    double R1,R2;
    cin>>R1>>R2;
    double R=1.0/(1.0/R1+1.0/R2);
    cout<<pyround(R,2)<<endl;
    return 0;
}