#include<bits/stdc++.h>
#define ll long long
#define ull unsigned long long
#define maxn 205
#define put() putchar('\n')
#define Tp template<typename Ty>
#define Ts template<typename Ty,typename... Ar>
using namespace std;
void read(int &x){
    int f=1;x=0;char c=getchar();
    while (c<'0'||c>'9') {if (c=='-') f=-1;c=getchar();}
    while (c>='0'&&c<='9') {x=x*10+c-'0';c=getchar();}
    x*=f;
}
namespace Debug{
	Tp void _debug(char* f,Ty t){cerr<<f<<'='<<t<<endl;}
	Ts void _debug(char* f,Ty x,Ar... y){while(*f!=',') cerr<<*f++;cerr<<'='<<x<<",";_debug(f+1,y...);}
	Tp ostream& operator<<(ostream& os,vector<Ty>& V){os<<"[";for(auto& vv:V) os<<vv<<",";os<<"]";return os;}
	#define gdb(...) _debug((char*)#__VA_ARGS__,__VA_ARGS__)
}using namespace Debug;
#define fi first
#define se second
#define mk make_pair
const int mod=1e9+7;
int power(int x,int y=mod-2) {
	int sum=1;
	while (y) {
		if (y&1) sum=sum*x%mod;
		x=x*x%mod;y>>=1;
	}
	return sum;
}
int n;
long double f[maxn][maxn][maxn],ans;
signed main(void){
	int i,j,k,l;
	read(n);
	f[n][0][0]=1;double N=n*n;
	for (i=n;i>=0;i--) {
		for (j=n-i;j>=0;j--) {
//			gdb(i,j,l);
			for (l=0;l<=j;l+=2) {
				k=n-i-j;
				double p1=1.0*i*(i-1)/N,p2=2.0*i*l/N,p3=2.0*i*(j-l)/N;
				double p4=2.0*l*(j-l)/N,p5=1.0*l*(l-2)/N,p6=1.0*(j-l)*(j-l-1)/N,P=p1+p2+p3+p4+p5+p6;
//				gdb(i,j,l,P,p1,p2,p3,p4,p5,p6,f[i][j][l]);
				if (P>1e-9) {
					if (i>=2) f[i-2][j+2][l+2]+=f[i][j][l]*p1/P;
					if (l>=2&&i>=1) f[i-1][j][l-2]+=f[i][j][l]*p2/P;
					if (i>=1) f[i-1][j][l]+=f[i][j][l]*p3/P;
					if (j>=2&&l>=2) f[i][j-2][l-2]+=f[i][j][l]*p4/P;
					if (j>=2&&l>=4) f[i][j-2][l-4]+=f[i][j][l]*p5/P;
					if (j>=2) f[i][j-2][l]+=f[i][j][l]*p6/P;
					ans+=f[i][j][l]/P;				
				}
//				gdb(f[0][0][0]);
			}
		}
	}
	printf("%.9Lf",ans);
	return 0;
}