#include<bits/stdc++.h>
#define Yukinoshita namespace
#define Yukino std
using Yukinoshita Yukino;
int read()
{
	int s=0,w=1;
	char ch=getchar();
	while(ch<'0'||ch>'9') w=ch=='-'?-1:1,ch=getchar();
	while(ch>='0'&&ch<='9') s=s*10+ch-'0',ch=getchar();
	return s*w;
}
double dp[205][205][205];//有x条非平凡链，y个孤点，z个二元链 
/*
非平凡链合并：4x^2-2x,x-=1
非平凡链加孤点：4xy,y-=1
非平凡链加二元链：8xz,z-=1
孤点加孤点：y^2-y, y-=2,z+=1
孤点加二元链：4yz，x+=1,y-=1,z-=1
二元链合并：4z^2-4z,x+=1,z-=2 
*/
int main()
{
	int n=read(),x,y,z,sum;
	double ans=0;
	for(sum=0;sum<=n;sum++)
		for(x=0;x<=sum;x++)
			for(y=0;x+y<=sum;y++)
			{
				z=sum-x-y;
				if(x*3+y+z*2>n) continue;
				double fm=4*x*x-2*x+4*x*y+8*x*z+(y-1)*y+4*y*z+4*z*z-4*z,v=n*n/fm,tp;
				if(!fm) continue;
				if(x)
					dp[x][y][z]+=dp[x-1][y][z]*(4*x*x-2*x)/fm;
				if(y)
					dp[x][y][z]+=dp[x][y-1][z]*4*x*y/fm;
				if(z)
					dp[x][y][z]+=dp[x][y][z-1]*8*x*z/fm;
				if(y>=2)
					dp[x][y][z]+=dp[x][y-2][z+1]*(y-1)*y/fm;
				if(y&&z)
					dp[x][y][z]+=dp[x+1][y-1][z-1]*4*y*z/fm;
				if(z>=2)
					dp[x][y][z]+=dp[x+1][y][z-2]*(4*z*z-4*z)/fm;
				dp[x][y][z]+=v;
//				cout<<x<<' '<<y<<' '<<z<<':'<<fm<<' '<<dp[x][y][z]<<endl;
			}
	printf("%.8lf",dp[0][n][0]);
}