#include <bits/stdc++.h>
using namespace std;
typedef long double DB;

DB d,x,n;
int main() {
    cin>>n>>d>>x; DB ans=0;
    for(int i=n;i>=1;i--) {
        DB sum=(d*2*n+n*(2*n-1)*x);
        ans+=sum/2/n;
        DB d2=(d*(2*n-2)+d+2*x+3*d+3*x)/2/n;
        sum=sum-(4*d+4*n*x-2*x)/2/n;
        n-=1;
        DB x2=(sum-2*n*d2)/n/(2*n-1);
        d=d2; x=x2;
    } printf("%.15f\n",(double)ans);
}