#include<bits/stdc++.h>
#define reg register
#define ll long long
#define inf 0x3f3f3f3f3f3f3f3f
using namespace std;
int n;
double d,x,ans;
int main()
{
    cin>>n>>d>>x;
    for(reg int i=n;i;i--)
    {
        ans+=d+i*x-0.5*x;
        d=((i*2+2)*d+x*5)/i/2;
        x=(i*2+4)*x/i/2;
    }
    cout<<fixed<<setprecision(9)<<ans;
    return 0;
}