#include <bits/stdc++.h>

using namespace std;

#define fore(i, a, b) for(ll i = a, bella = b; i < bella; i++)
#define mset(a, b) memset(a, b, sizeof(a))
#define ALL(a) a.begin(), a.end()
#define SZ(a) ll(a.size())
#define fst first
#define snd second
#define pb push_back
#define FIO ios::sync_with_stdio(0); cin.tie(0); cout.tie(0)

typedef long double ld;
typedef long long ll;
typedef pair<ll, ll> ii;
typedef vector<ll> vi;

const ll MAXN = 15;
ll w[MAXN][MAXN], n;
ld v[MAXN], sum[MAXN];

ld calc() {
    ld ret = 0;
    fore(i, 0, n) fore(j, i + 1, n) ret += v[i] * v[j] * ld(w[i][j]);
    return ret;
}

void upd(ll a, ll b) {
    ld s = 0, e = v[a] + v[b];
    ll it = 50;
    while(it--) {
        ld m0 = (s * 2.0 + e) / 3.0, m1 = (s + e * 2.0) / 3.0;
        
        ld a0 = m0, b0 = v[a] + v[b] - a0;
        ld a1 = m1, b1 = v[a] + v[b] - a1;

        ld c0 = a0 * sum[a] + b0 * sum[b] + ld(w[a][b]) * (2.0 * a0 * b0 - a0 * v[b] - v[a] * b0);
        ld c1 = a1 * sum[a] + b1 * sum[b] + ld(w[a][b]) * (2.0 * a1 * b1 - a1 * v[b] - v[a] * b1);

        if(c0 > c1) e = m1;
        else s = m0;
    }

    sum[a] = sum[b] = 0;
    fore(i, 0, n) if(i != a && i != b) sum[i] -= v[a] * ld(w[i][a]) + v[b] * ld(w[i][b]);

    ld nwA = s, nwB = v[a] + v[b] - nwA;
    v[a] = nwA, v[b] = nwB;

    fore(i, 0, n) {
        sum[a] += v[i] * ld(w[a][i]);
        sum[b] += v[i] * ld(w[b][i]);

        if(i != a && i != b) sum[i] += v[a] * ld(w[i][a]) + v[b] * ld(w[i][b]);
    }
}

int main() { FIO;

    cin >> n;
    fore(i, 0, n) fore(j, 0, n) cin >> w[i][j];

    fore(i, 0, n) v[i] = 1.0/ld(n);

    auto cl=clock();
    while(ld(clock() - cl)/CLOCKS_PER_SEC < 0.99) {
        ll a = rand() % n, b = a;
        while(a == b) b = rand() % n;

        upd(a, b);
    }

    cout << fixed << setprecision(12) << calc() << '\n';

    return 0;
}