#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pii pair<int, int>
#define ull unsigned ll
#define f first
#define s second
#define ALL(x) x.begin(),x.end()
#define SZ(x) (int)x.size()
#define SQ(x) (x)*(x)
#define MN(a,b) a = min(a,(__typeof__(a))(b))
#define MX(a,b) a = max(a,(__typeof__(a))(b))
#define pb push_back
#define REP(i,n) for (int i = 0; i<n; ++i)
#define REP1(i,n) for (int i = 1; i<=n; ++i)
#define SORT_UNIQUE(c) (sort(c.begin(),c.end()), c.resize(distance(c.begin(),unique(c.begin(),c.end()))))
#ifdef BALBIT
#define IOS()
#define bug(...) fprintf(stderr,"#%d (%s) = ",__LINE__,#__VA_ARGS__),_do(__VA_ARGS__);
template<typename T> void _do(T &&x){cerr<<x<<endl;}
template<typename T, typename ...S> void _do(T &&x, S &&...y){cerr<<x<<", ";_do(y...);}
#else
#define IOS() ios_base::sync_with_stdio(0);cin.tie(0);
#define endl '\n'
#define bug(...)
#endif

const int iinf = 1e9+10;
const ll inf = 1ll<<60;
const ll mod = 1e9+7 ;


void GG(){cout<<"0\n"; exit(0);}

ll mpow(ll a, ll n, ll mo = mod){ // a^n % mod
    ll re=1;
    while (n>0){
        if (n&1) re = re*a %mo;
        a = a*a %mo;
        n>>=1;
    }
    return re;
}

ll inv (ll b, ll mo = mod){
    if (b==1) return b;
    return (mo-mo/b) * inv(mo%b,mo) % mo;
}

const int maxn = 1e2+5;

vector<int> g[maxn];
bool sn[maxn];
int c = 0;
void dfs(int v) {
    sn[v] = 1; ++c;
    for (int u : g[v]) {
        if (!sn[u]) {
            dfs(u);
        }
    }
}
signed main(){
    IOS();

    int n; cin>>n;
    REP(i,n) {
        REP(j,n) {
            char c; cin>>c;
            if (c == '1') {
                g[j].pb(i);
            }
        }
    }
    double re = 0;
    REP(i,n) {
        memset(sn, 0, sizeof sn);
        c = 0;
        dfs(i);
        double cb = 1;
        re += 1/(double)c;
    }
    cout<<fixed<<setprecision(12)<<re<<endl;
}

#include<bits/stdc++.h>
#define int long long
using namespace std;
int N;
vector<int> G[110];
signed main(){
  cin>>N;
  for(int i=0;i<N;i++)
    for(int j=0;j<N;j++){
      char c;
      cin>>c;
      if(c=='1')G[j].push_back(i);
    }
  long double ans=0;
  for(int i=0;i<N;i++){
    vector<bool> B(N,false);
    B[i]=true;
    queue<int> Q;
    Q.push(i);
    int cnt=1;
    while(!Q.empty()){
      int I=Q.front();
      Q.pop();
      for(int i:G[I])
        if(!B[i]){
          B[i]=true;
          cnt++;
          Q.push(i);
        }
    }
    ans+=(long double)1/(long double)cnt;
  }
  cout<<fixed<<setprecision(16)<<ans<<endl;
}