#include <bits/stdc++.h>
using namespace std;

#define MAX 128

double R[2*MAX][MAX][MAX];
int B[2*MAX][MAX][MAX];
int n;

double f(int c0, int c1, int c2)
{
    if(c0 < 0 || c1 < 0 || c2 < 0) return 0;
    double &res = R[c0][c1][c2];
    if(B[c0][c1][c2] != 0) return res;
    B[c0][c1][c2] = 1;

    int a = c0*(c0 - 1);
    int b = 4*c0*c1;
    int c = 4*c0*c2;
    int d = 4*c1*(c1 - 1);
    int e = 8*c1*c2;
    int g = 2*c2*(2*c2 - 1);
    int t = n*n;
    if(a + b + c + d + e + g == 0) return res;
    return res = (t 
            + a*f(c0 - 2, c1 + 1, c2) 
            + b*f(c0 - 1, c1 - 1, c2 + 1) 
            + c*f(c0 - 1, c1, c2)
            + d*f(c0, c1 - 2, c2 + 1)
            + e*f(c0, c1 - 1, c2)
            + g*f(c0, c1, c2 - 1)
        )/(a + b + c + d + e + g + 0.0);
}

void solve(int test)
{
    cin >> n;
    cout << fixed << setprecision(11) << f(n, 0, 0);
}

int main()
{
    int t = 1;
    //cin >> t;
    for(int i = 0; i < t; ++i)
        solve(i);
    return 0;
}