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


#define li          long long int
#define rep(i,to)   for(li i=0;i<((li)(to));i++)
#define repp(i,start,to)    for(li i=(li)(start);i<((li)(to));i++)
#define pb          push_back
#define sz(v)       ((li)(v).size())
#define bgn(v)      ((v).begin())
#define eend(v)     ((v).end())
#define allof(v)    (v).begin(), (v).end()
#define dodp(v,n)       memset(v,(li)n,sizeof(v))
#define bit(n)      (1ll<<(li)(n))
#define mp(a,b)     make_pair(a,b)
#define rin rep(i,n)
#define EPS 1e-12
#define ETOL 1e-8
#define MOD 1000000007
typedef pair<li, li> PI;

#define INF bit(60)

#define DBGP 1


#define idp if(DBGP)
#define F first
#define S second
#define p2(a,b)     idp cout<<a<<"\t"<<b<<endl
#define p3(a,b,c)       idp cout<<a<<"\t"<<b<<"\t"<<c<<endl
#define p4(a,b,c,d)     idp cout<<a<<"\t"<<b<<"\t"<<c<<"\t"<<d<<endl
#define p5(a,b,c,d,e)       idp cout<<a<<"\t"<<b<<"\t"<<c<<"\t"<<d<<"\t"<<e<<endl
#define p6(a,b,c,d,e,f)     idp cout<<a<<"\t"<<b<<"\t"<<c<<"\t"<<d<<"\t"<<e<<"\t"<<f<<endl
#define p7(a,b,c,d,e,f,g)       idp cout<<a<<"\t"<<b<<"\t"<<c<<"\t"<<d<<"\t"<<e<<"\t"<<f<<"\t"<<g<<endl
#define p8(a,b,c,d,e,f,g,h)     idp cout<<a<<"\t"<<b<<"\t"<<c<<"\t"<<d<<"\t"<<e<<"\t"<<f<<"\t"<<g<<"\t"<<h<<endl
#define p9(a,b,c,d,e,f,g,h,i)       idp cout<<a<<"\t"<<b<<"\t"<<c<<"\t"<<d<<"\t"<<e<<"\t"<<f<<"\t"<<g<<"\t"<<h<<"\t"<<i<<endl
#define p10(a,b,c,d,e,f,g,h,i,j)        idp cout<<a<<"\t"<<b<<"\t"<<c<<"\t"<<d<<"\t"<<e<<"\t"<<f<<"\t"<<g<<"\t"<<h<<"\t"<<i<<"\t"<<j<<endl
#define foreach(it,v)   for(__typeof((v).begin()) it=(v).begin(); it!=(v).end(); ++it)
#define p2p(x)      idp p2((x).F, (x).S)
#define dump(x,n)   idp{rep(i,n){cout<<x[i]<<" ";}puts("");}
#define dump2(x,n)  idp{rep(i,n){cout<<"["<<x[i].F<<" , "<<x[i].S<<"] ";}puts("");}
#define dumpi(x)    idp{foreach(it, x){cout<<(*it)<<" ";}puts("");}
#define dumpi2(x)   idp{foreach(it, x){cout<<"["<<(it)->F<<" , "<<(it)->S<<"] ";}puts("");}

#define read2d(a,w,h)   rep(i,h)rep(j,w)cin>>a[i][j]
#define dump2d(a,w,h)   rep(i,h){rep(j,w)cout<<a[i][j]<<" ";puts("");}

typedef pair<li, li> PI;

li n;
vector<li> edges[111];

unordered_map<bitset<110>, double> memo;

inline set<li> visit(li root) {
    queue<li> q;
    q.push(root);
    set<li> res;
    while (!q.empty()) {
        li now = q.front();
        q.pop();
        if (res.count(now) > 0) {
            continue;
        }
        res.insert(now);
        for (auto next : edges[now]) {
            q.push(next);
        }
    }
    return res;
}


int main() {
    cin >> n;
    rin{
        string s;
        cin >> s;
        rep(j, n) {
            if (s[j] == '1') {
                edges[i].pb(j);
            }
        }
    }

    vector<li> deletable(n);
    rin{
        for (auto v : visit(i)) {
            deletable[v]++;
        }
    }
    double res = 0.0;
    rin{
        res += 1.0 / deletable[i];
    }
    printf("%.12f\n", res);


    return 0;
}
#pragma GCC optimize("Ofast,unroll-loops,fast-math")
#include<bits/stdc++.h>
using namespace std;
typedef long long ll ;
#define pll pair<ll , ll >
#define all(x) (x).begin(),(x).end()
#define sz(x) (ll)(x).size()
#define X   first
#define Y   second
#define mp  make_pair
#define pii pair<int , int>
#define vec vector
#define file_io freopen("input.txt", "r", stdin);freopen("output.txt", "w", stdout);
#define migmig ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define pb push_back
ll poww(ll a, ll b, ll md) {
    return (!b ? 1 : (b & 1 ? a * poww(a * a % md, b / 2, md) % md : poww(a * a % md, b / 2, md) % md));
}
const int maxn = 100+5 ;
const ll inf = 9223372036854775807 ;
const ll mod = 1e9 + 7 ;
ll n , cnt , mark[maxn] ; 
vec<int> adj[maxn] ; 
string s[maxn] ; 
long double ans ; 
void dfs(int v){
	cnt++ ; 
	mark[v] = 1 ; 
	for(auto u : adj[v]) if(!mark[u]) dfs(u) ; 
}
int main()
{
	migmig ;
	cin>>n ; 
	for(int i = 1 ; i  <= n ; i ++ ){
		cin>>s[i] ; 
		s[i] = '#' + s[i] ; 
		for(int j = 1 ; j <= n ; j ++ ){
			if(s[i][j] == '1'){
				adj[j].pb(i) ; 
			}
		}
	}
	for(int i = 1 ; i <= n ; i ++ ){
		dfs(i) ; 
		ans += 1/(long double)(cnt) ; 
		cnt = 0 ; 
		memset(mark , 0 , sizeof mark) ; 
	}
	cout<<fixed<<setprecision(9)<<ans ; 
}








