#include<cstdio>
#include<algorithm>
#include<iostream>
#define fo(i,a,b) for(i=a;i<=b;i++)
using namespace std;
typedef long double db;
db a,p,ans;
int i,j,k,l,t,n,m;
int main(){
    cin>> n >> a >> p;
    a-=p;
    t=2*n;
    l=n;
    fo(i,1,n){
        ans+=(db)(a*t+p*t*(t+1)/2)/t;
        a=a+a/l+3*p/(2*l);
        p=p+2*p/l;
        l--;
        t-=2;
    }
    printf("%.15lf\n",ans);
}
