#include <iostream.h>

class Dientro{
private:
        float r;
public:
       void Nhapgiatri(float Ri){
            r=Ri;
       }
       //Tinh dien tro song song cua 2 dien tro la R2 va dien tro hien tai
       Dientro TinhDTTD(Dientro R2){
               Dientro rtd;
               rtd.r = 1/(1/r+ 1/R2.r);
               return rtd;
               
       }
       //Tinh dien tro song song cua n dien tro trong mang R2
       Dientro TinhDTTD(Dientro R2[], int n){
               Dientro rtd=R2[0];
               for (int i=1;i<n;i++)
                   rtd = rtd.TinhDTTD(R2[i]);
               return rtd;
               
       }
       void Inra(){
            cout<<r<<endl;
       }
              
};
int main(){
    Dientro r1,r2,r3;
    r1.Nhapgiatri(10);
    r2.Nhapgiatri(20);
    r3.Nhapgiatri(30);
    r1.Inra();
    r2.Inra();
    r3.Inra();
    
    Dientro r = (r1.TinhDTTD(r2)).TinhDTTD(r3);
    r.Inra();

    const int N=20; 
    Dientro ra[N];
    for (int i=0;i<N;i++){
        ra[i].Nhapgiatri(10+10*i);
        
    }
    r = r1.TinhDTTD(ra,N);
    r.Inra();
    
    system("Pause");
}