#include <bits/stdc++.h>
#define For(i, a, b) for(i32 i = (a), endi = (b); i <= endi; ++i)
#define foR(i, a, b) for(i32 i = (a), endi = (b); i >= endi; --i)
using namespace std;

template<typename T, typename U>
void chkmin(T &a, U b) { if(a > b) a = b; }

using i32 = int;
using i64 = long long;
using f64 = long double;

int mp[128];
void init()
{
    For(i, '0', '9') mp[i] = i - '0';
    For(i, 'a', 'z') mp[i] = i - 'a' + 10;
}

void solve()
{
    i32 n;
    cin >> n;
    vector dp(n+1, vector(n+1, vector<f64>(n+1, 0))); // 孤点 单链 长链
    dp[n][0][0] = 0;
    i32 tmp = n * n;
    auto dfs = [&](auto &&self, i32 a, i32 b, i32 c) -> f64
    {
        if (!c && a + b < 2) return 0;
        if(dp[a][b][c] > 1e-6) return dp[a][b][c];
        f64 s1 = a * (a - 1), s2 = a * b * 4, s3 = a * c * 4, 
            s4 = b * 2 * (b * 2 - 2), s5 = b * c * 8, s6 = c * 2, s7 = c * 2 * (c * 2 - 2);
        f64 res = (s1 + s2 + s3 + s4 + s5 + s6 + s7) / tmp;
        if (a > 1) dp[a][b][c] += self(self, a - 2, b + 1, c) * s1 /tmp;
        if (a && b) dp[a][b][c] += self(self, a - 1, b - 1, c + 1) * s2 / tmp;
        if (a && c) dp[a][b][c] += self(self, a - 1, b, c) * s3 / tmp;
        if (b > 1) dp[a][b][c] += self(self, a, b - 2, c + 1) * s4 / tmp;
        if (c && b) dp[a][b][c] += self(self, a, b - 1, c) * s5 / tmp;
        if (c) dp[a][b][c] += self(self, a, b, c - 1) * s6 / tmp;
        if (c > 1) dp[a][b][c] += self(self, a, b, c - 1) * s7 / tmp;
        dp[a][b][c] = (dp[a][b][c] + 1) / res;
        return dp[a][b][c];
    };
    cout << std::format("{:.9f}\n", dfs(dfs, n, 0, 0));
}

int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    init();
    i32 T = 1;
    // cin >> T;
    while(T--) solve();
    return 0;
}