//Solution by lukasP (Lukáš Poláček)
#include <iostream>
#include <vector>
#include <string>
#include <set>
#include <unordered_set>
#include <algorithm>
#include <sstream>
#include <queue>
#include <bitset>
#include <utility>
#include <list>
#include <numeric>

#include <cstdio>
#include <cstring>
#include <cmath>
#include <cctype>

#define rep(i,a,b) for(__typeof(b) i=(a); (i)<(b); ++(i))

int main() {
  int n; scanf("%d", &n);
  std::vector<std::vector<int>> orig(n);
  std::vector<std::unordered_set<int>> op(n);
  rep(i,1,n) {
    std::string s;
    std::cin >> s;
    rep(j,0,i) {
      if (s[j] == '1') {
        orig[i].push_back(j);
        op[j].insert(i);
      } else {
        orig[j].push_back(i);
        op[i].insert(j);
      }
    }
  }

  std::vector<int> g(n);
  std::vector<bool> winners(n, false);
  int current = 0, worst = 0;
  rep(i,0,n) {
    int best = -1;
    rep(j,0,n) if (!winners[j]) {
      if (best == -1 || g[j] + op[best].size() > g[best] + op[j].size()) {
        best = j;
      }
    }

    winners[best] = true;
    current -= g[best];
    for (int x : op[best]) if (!winners[x]) {
      ++g[x];
      ++current;
    }
    for (int x : orig[best]) if (!winners[x]) {
      op[x].erase(best);
    }
    worst = std::max(current, worst);
  }
  std::cout << worst << std::endl;
}