杭電 2009 求數列的和

#include<cstring>
#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cmath>
using namespace std;
double n,m;
double digui(int ci);
int main(){
    while(scanf("%lf %lf",&n,&m)!=EOF){
        double sum=0;
        for(int i=1;i<=m;i++){
            sum+=digui(i);  
        }
        printf("%.2lf\n",sum);
    } 
}
double digui(int ci){
    if(ci==1){
        return n;
    } else{
        return sqrt(digui(ci-1));
    }
}