#include <bits/stdc++.h>
using namespace std;
//#pragma GCC optimize("Ofast")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
 
#define ms(s, n) memset(s, n, sizeof(s))
#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define FORd(i, a, b) for (int i = (a) - 1; i >= (b); --i)
#define FORall(it, a) for (__typeof((a).begin()) it = (a).begin(); it != (a).end(); it++)
#define sz(a) int((a).size())
#define present(t, x) (t.find(x) != t.end())
#define all(a) (a).begin(), (a).end()
#define uni(a) (a).erase(unique(all(a)), (a).end())
#define pb push_back
#define pf push_front
#define mp make_pair
#define fi first
#define se second
#define prec(n) fixed<<setprecision(n)
#define bit(n, i) (((n) >> (i)) & 1)
#define bitcount(n) __builtin_popcountll(n)
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<int, int> pi;
typedef vector<int> vi;
typedef vector<pi> vii;
const int MOD = (int) 1e9 + 7;
const int FFTMOD = 119 << 23 | 1;
const int INF = (int) 1e9 + 23111992;
const ll LINF = (ll) 1e18 + 23111992;
const ld PI = acos((ld) -1);
const ld EPS = 1e-9;
inline ll gcd(ll a, ll b) {ll r; while (b) {r = a % b; a = b; b = r;} return a;}
inline ll lcm(ll a, ll b) {return a / gcd(a, b) * b;}
inline ll fpow(ll n, ll k, int p = MOD) {ll r = 1; for (; k; k >>= 1) {if (k & 1) r = r * n % p; n = n * n % p;} return r;}
template<class T> inline int chkmin(T& a, const T& val) {return val < a ? a = val, 1 : 0;}
template<class T> inline int chkmax(T& a, const T& val) {return a < val ? a = val, 1 : 0;}
inline ull isqrt(ull k) {ull r = sqrt(k) + 1; while (r * r > k) r--; return r;}
inline ll icbrt(ll k) {ll r = cbrt(k) + 1; while (r * r * r > k) r--; return r;}
inline void addmod(int& a, int val, int p = MOD) {if ((a = (a + val)) >= p) a -= p;}
inline void submod(int& a, int val, int p = MOD) {if ((a = (a - val)) < 0) a += p;}
inline int mult(int a, int b, int p = MOD) {return (ll) a * b % p;}
inline int inv(int a, int p = MOD) {return fpow(a, p - 2, p);}
inline int sign(ld x) {return x < -EPS ? -1 : x > +EPS;}
inline int sign(ld x, ld y) {return sign(x - y);}
mt19937 mt(chrono::high_resolution_clock::now().time_since_epoch().count());
inline int mrand() {return abs((int) mt());}
inline int mrand(int k) {return abs((int) mt()) % k;}
#define db(x) cerr << "[" << #x << ": " << (x) << "] ";
#define endln cerr << "\n";

void chemthan() {
    int n; cin >> n;
    vector<string> s(n);
    FOR(i, 0, n) cin >> s[i];
    vector<vi> g(n, vi(n));
    FOR(i, 0, n) g[i][i] = 1;
    FOR(i, 0, n) FOR(j, 0, n) if (i != j) {
        g[i][j] = s[i][j] == '1';
    }
    FOR(k, 0, n) FOR(i, 0, n) FOR(j, 0, n) {
        g[i][j] |= g[i][k] & g[k][j];
    }
    double res = 0;
    FOR(i, 0, n) {
        int num = 0;
        FOR(j, 0, n) if (i ^ j) {
            if (g[j][i]) {
                num++;
            }
        }
        res += 1.0 / (num + 1);
    }
    cout << prec(9) << res << "\n";
}

int32_t main(int32_t argc, char* argv[]) {
    ios_base::sync_with_stdio(0), cin.tie(0);
    if (argc > 1) {
        assert(freopen(argv[1], "r", stdin));
    }
    if (argc > 2) {
        assert(freopen(argv[2], "wb", stdout));
    }
    chemthan();
    cerr << "\nTime elapsed: " << 1000 * clock() / CLOCKS_PER_SEC << "ms\n";
    return 0;
}

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

const int N = 100+19;
int g[N][N],vis[N],val[N],n;

void dfs(int u) {
  ++val[u];
  vis[u] = 1;
  for(int i = 1 ; i <= n ; ++i) 
    if(g[u][i] && !vis[i])
      dfs(i);
}

void solve() {
  cin >> n;
  for(int i = 1 ; i <= n ; ++i) {
    string s;
    cin >> s;
    for(int j = 1 ; j <= n ; ++j)
      if(s[j-1] == '1') 
        g[i][j] = 1;
  }

  for(int i = 1 ; i <= n ; ++i) {
    for(int j = 1 ; j <= n ; ++j) vis[j] = 0;
    dfs(i);
  }
  double ans = 0;
  for(int i = 1 ; i <= n ; ++i) ans += 1.0 / val[i];

  printf("%.12lf\n",ans);
}

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