#include<cstdio>
#include<cstring>
#include<algorithm>
#define rep(i,a,b) for(i=a;i<=b;i++)
using namespace std;
typedef long double ld;
int main(){
//	freopen("a.in","r",stdin);
//	freopen("a.out","w",stdout);
	int n,k1,k2;int i;
	ld a,x,m;ld ans=0.;
	scanf("%d%d%d",&n,&k1,&k2);k1-=k2; 
	a=k1;x=k2;m=2.*n;
	rep(i,1,n){
		ans+=a+(m+1)/2.*x;
		a+=(2.*a+3.*x)/m;
		//a=((m+2.)*a+3.*x)/(ld)m;
		x+=4.*x/m;
		//x=x*(m+4)/(ld)m;
		m-=2.;
	}
	printf("%.15f",(double)ans);
}
		
	
	