#include <iostream>
#include <stack>

using namespace std;

#define rep(i,n) for(int i=0;i<(n);++i)
#define out(v) cout<<v<<"\n"
const int INF = 1e6;

int main() {
  cin.tie(0); ios::sync_with_stdio(false);
  int N; cin >> N;

  bool edge[N][N];
  rep(i, N) rep(j, N) {
    char c; cin >> c;
    edge[i][j] = (c == '1');
  }

  int d[N][N];
  rep(i, N) rep(j, N) d[i][j] = edge[i][j] ? 1 : INF;
  rep(k, N) rep(i, N) rep(j, N) {
    d[i][j] = min(d[i][j], d[i][k] + d[k][j]);
  }

  int color[N];
  rep(i, N) color[i] = INF;
  color[0] = 0;

  stack<int> st;
  st.push(0);
  while (!st.empty()) {
    int p = st.top(); st.pop();
    rep(i, N) {
      if (!edge[i][p])
        continue;
      if (color[i] == color[p]) {
        out(-1);
        return 0;
      }
      if (color[i] == INF) {
        color[i] = 1 - color[p];
        st.push(i);
      }
    }
  }

  int r = 0;
  rep(i, N) rep(j, N) {
    if (i == j)
      continue;
    r = max(r, d[i][j]);
  }
  out(r+1);
  return 0;
}
