#include<cstdio>
#include<iostream>
#define rep(i,s,t) for (int i=s;i<=t;++i)
using namespace std;
double ans=0;
void dfs(int n,double d,double x){
    if (n==0) return;
    ans+=double(2*n*d+x*n*(2*n+1))/(2*n);
    d=d+d/n+3*x/(2*n);
    x=x+2*x/n;
    dfs(n-1,d,x);
}
int main()
{
    int n;
    double d,x;scanf("%d%lf%lf",&n,&d,&x);
    d-=x;
    dfs(n,d,x);
    printf("%.15f\n",ans);
    return 0;
}
