#include <bits/stdc++.h>
using namespace std;
using lint = long long int;
using P = pair<int, int>;
using PL = pair<lint, lint>;
#define FOR(i, begin, end) for(int i=(begin),i##_end_=(end);i<i##_end_;i++)
#define IFOR(i, begin, end) for(int i=(end)-1,i##_begin_=(begin);i>=i##_begin_;i--)
#define REP(i, n) FOR(i,0,n)
#define IREP(i, n) IFOR(i,0,n)
#define ALL(a)  (a).begin(),(a).end()
constexpr int MOD = 1000000007;
constexpr lint B1 = 1532834020;
constexpr lint M1 = 2147482409;
constexpr lint B2 = 1388622299;
constexpr lint M2 = 2147478017;
constexpr int INF = 2147483647;
void yes(bool expr) {cout << (expr ? "Yes" : "No") << "\n";}
template<class T>void chmax(T &a, const T &b) { if (a<b) a=b; }
template<class T>void chmin(T &a, const T &b) { if (b<a) a=b; }
struct Node;
vector<Node> V;
struct Node {
  vector<int> nbr;
  bool vst = false;
  int val = 0;
  void dfs() {
    vst = true;
    val++;
    for(int x : nbr) if(!V[x].vst) V[x].dfs();
  }
};
int main()
{
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int N;
  cin >> N;
  REP(i, N) V.emplace_back();
  REP(i, N) {
    string S;
    cin >> S;
    REP(j, N) {
      if(S[j] == '1') {
        V[i].nbr.push_back(j);
      }
    }
  }
  double ans = 0;
  REP(i, N) {
    REP(j, N) V[j].vst = false;
    V[i].dfs();
  }
  REP(i, N) ans += 1.0 / V[i].val;
  cout << fixed << setprecision(10) << ans << "\n";

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

using ll = long long;
using Vi = std::vector<int>;
using Vl = std::vector<ll>;
using Pii = std::pair<int, int>;
using Pll = std::pair<ll, ll>;

constexpr int I_INF = std::numeric_limits<int>::max();
constexpr ll L_INF = std::numeric_limits<ll>::max();

template <typename T1, typename T2>
inline bool chmin(T1& a, const T2& b) {
    if (a > b) {
        a = b;
        return true;
    }
    return false;
}
template <typename T1, typename T2>
inline bool chmax(T1& a, const T2& b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}

template <ostream& os = std::cout>
class Prints {
private:
    class __Prints {
    public:
        __Prints(const char* sep, const char* term) : sep(sep), term(term) {}
        template <class... Args>
        auto operator()(const Args&... args) const -> decltype((os << ... << std::declval<Args>()), void()) { print(args...); }
        template <typename T>
        auto pvec(const T& vec, size_t sz) const -> decltype(os << std::declval<decltype(std::declval<T>()[0])>(), void()) {
            for (size_t i = 0; i < sz; i++)
                os << vec[i] << (i == sz - 1 ? term : sep);
        }
        template <typename T>
        auto pmat(const T& mat, size_t h, size_t w) -> decltype(os << std::declval<decltype(std::declval<T>()[0][0])>(), void()) {
            for (size_t i = 0; i < h; i++)
                for (size_t j = 0; j < w; j++)
                    os << mat[i][j] << (j == w - 1 ? term : sep);
        }

    private:
        const char *sep, *term;
        void print() const { os << term; }
        void print_rest() const { os << term; }
        template <class T, class... Tail>
        void print(const T& head, const Tail&... tail) const { os << head, print_rest(tail...); }
        template <class T, class... Tail>
        void print_rest(const T& head, const Tail&... tail) const { os << sep << head, print_rest(tail...); }
    };

public:
    Prints() {}
    __Prints operator()(const char* sep = " ", const char* term = "\n") const { return __Prints(sep, term); }
};

Prints<> prints;
Prints<std::cerr> prints_err;

//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

void solve() {
    int N;
    cin >> N;
    static bool reachable[100][100] = {};
    for (ll i = 0; i < N; i++) {
        reachable[i][i] = true;
    }
    for (ll i = 0; i < N; i++) {
        string s;
        cin >> s;
        for (ll j = 0; j < N; j++) {
            if (s[j] == '1') reachable[i][j] = true;
        }
    }
    for (ll k = 0; k < N; k++) {
        for (ll i = 0; i < N; i++) {
            for (ll j = 0; j < N; j++) {
                reachable[i][j] |= reachable[i][k] & reachable[k][j];
            }
        }
    }
    double ans = 0.0;
    for (ll i = 0; i < N; i++) {
        ll cnt = 0;
        for (ll j = 0; j < N; j++) {
            if (reachable[j][i]) ++cnt;
        }
        ans += 1.0 / cnt;
    }
    prints()(ans);
}

//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

int main() {
#ifdef FASTIO
    std::cin.tie(nullptr), std::cout.tie(nullptr);
    std::ios::sync_with_stdio(false);
#endif
#ifdef FILEINPUT
    std::ifstream ifs("./in_out/input.txt");
    std::cin.rdbuf(ifs.rdbuf());
#endif
#ifdef FILEOUTPUT
    std::ofstream ofs("./in_out/output.txt");
    std::cout.rdbuf(ofs.rdbuf());
#endif
    std::cout << std::setprecision(18) << std::fixed;
    solve();
    std::cout << std::flush;
    return 0;
}