//#pragma GCC optimize(3)
#include<bits/stdc++.h>
#define SZ(x) ((int)x.size())
#define uni(x) sort(all(x)),x.resize(unique(all(x))-x.begin());
#define GETPOS(c,x) (lower_bound(all(c),x)-c.begin())
#define lown1(x,val) low(in(x),val)-x
#define lowm1(x,val) low(im(x),val)-x
#define low1(x,nums,val) low(x+1,x+nums+1,val)-x
#define mst(x,val) memset((x),val,sizeof((x)))
#define ls rt<<1
#define rs rt<<1|1
#define lson rt<<1,l,M
#define rson rt<<1|1,M+1,r
#define PI acos(-1)
#define MM int M=(l+r)>>1;
#define fu(i,r,t) for(int i=r;i<=t;i++)
#define fd(i,r,t) for(int i=r;i>=t;i--)
#define fh(i,be,e) for(int i=head[be];~i;i=e[i].next)
#define fa(i,V) for(auto i:V)
#define far(i,V) for(auto &i:V)
#define IOS ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define lcm(a,b) ((a)*(b))/__gcd(a,b)
#define cp(i,ans) printf("%.if",ans);
#define cpp(i,ans) cout<<setprecision(i)<<fixed<<ans<<endl;
#define ppb pop_back
#define ppf pop_front
#define pb push_back
#define pf push_front
#define pq priority_queue
#define lowbit(x) ((x)&(-x))
#define all(V) V.begin(),V.end()
#define ms multiset
#define mod(x) (((x)<0)?(x)%mo_num+mo_num:(x)%mo_num)
#define vc vector
#define vct vector<int>
#define SET set<int>
#define dq deque<int>
#define out(i) cout<<(i)<<endl;
#define fi first
#define se second
#define fun(i) fu(i,1,n)
#define fut(i) fu(i,1,t)
#define fum(i) fu(i,1,m)
#define ld long double
#define umap unordered_map
#define Umap unordered_map<int,int>
#define P pair<int,int>
#define mk make_tuple
#define eps 1e-6
//Remember cancel"#define endl '\n'" in interactive questions or use "<<flush"
#define endl '\n'
#define low lower_bound
#define upp upper_bound
#define yn(key) out(key?"YES":"NO")
//#define yn(key) out(key?"Yes":"No")
#define in(i) i+1,i+1+n
#define im(i) i+1,i+1+m
#define ik(i,k) i+1,i+1+k
#define bffs(i) __builtin_ffs(i)
#define bcount(i) __builtin_popcount(i)
#define bone(i) ((1<<i)-1)
#define db double
#define ll long long
#define got(container,num) get<num-1>(container)
#define int long long
#define print(a,n) fun(i)cout<<a[i]<<(i!=n?' ':endl);
#define outcase(x) cout<<"Case #"<<(++case_of_T)<<": "<<(x)<<endl;
#define ptcase(x) printf("Case #%d: %d\n",++case_of_T,x);
#define plcase(x) printf("Case #%lld: %lld\n",++case_of_T,x);
using namespace std;
//Remember to cancel the line below and declare INT=INT_MAX/2; when you want to change long to int
const int INF=LLONG_MAX/4,SINF=0x3f3f3f3f,Lim=1<<20,MINF=LLONG_MAX;
//const int INF=INT_MAX/4,SINF=0x3f;
// use C:printf("%.16f", x);  ->  printf("%.10f", x); can accelerate the program
const int dx[]={0,0,-1,1},dy[]={-1,1,0,0};//down up left right
const int maxn=1e6+1e5;
int mo_num=1e9+7;
//const int mo_num=998244353;
int n,m,t,a[maxn],b[maxn],ans,case_of_T;
const int N=105;
int f[N][N];
void solve()
{
    cin>>n;
    mst(f,SINF);
    fun(i)
    {
        string k;cin>>k;
        f[i][i]=0;
        fun(j)
        {
            if(k[j-1]=='1')f[i][j]=1;
        }
    }
    for(int k=1;k<=n;k++){
        for(int i=1;i<=n;i++){
            for(int j=1;j<=n;j++){
                f[i][j]=min(f[i][j],f[i][k]+f[k][j]);
            }
        }
    }
    fun(i)fun(j)a[i]+=f[j][i]>100000?0:1;
    db Ans=0;
    fun(i)Ans+=(db)1/(db)a[i];
    cpp(11,Ans);
    return ;
}
main()
{
    IOS
    int T=1;
    //cin>>T;
    while(T--)solve();
    return 0;
}

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

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    int n; cin >> n;
    vector<string> s(n);
    vector<vector<int>> vis(n, vector<int>(n, 0));
    for (int i = 0; i < n; i++) {
        cin >> s[i];
        for (int j = 0; j < n; j++) {
            if (s[i][j] == '1') {
                vis[i][j] = 1;
            }
        }
        vis[i][i] = 1;
    }
    double ans = 0;
    for (int k = 0; k < n; k++) {
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) {
                if (vis[i][k] && vis[k][j]) {
                    vis[i][j] = 1;
                }
            }
        }
    }
    for (int i = 0; i < n; i++) {
        int num = 0;
        for (int j = 0; j < n; j++)
            num += vis[j][i];
        ans += 1.0 / num;
    }
    cout << fixed << setprecision(10) << ans;
    return 0;
}