// an overcomplicated solution
#include <bits/stdc++.h>
using namespace std;
const int oo = 1<<20;

int main(void) {
    int n;
    scanf("%d", &n);
    vector<vector<int>> Eout(n), Ein(n);
    for (int i = 1; i < n; ++i) {
        char w[n];
        scanf("%s", w);
        for (int j = 0; j < i; ++j) {
            int a = w[j] == '1' ? i : j, b = i+j-a;
            Eout[a].push_back(b);
            Ein[b].push_back(a);
        }
    }
    set<pair<int,int>> cost;
    vector<int> curcost(n);
    for (int i = 0; i < n; ++i) {
        curcost[i] = Eout[i].size();
        cost.insert(make_pair(Eout[i].size(), i));
    }
    int ans = 0, cur = 0;
    while (!cost.empty()) {
        cur += cost.begin()->first;
        ans = max(ans, cur);
        int i = cost.begin()->second;
        cost.erase(cost.begin());
        for (int j: Eout[i]) {
            if (curcost[j] < oo) {
                cost.erase(make_pair(curcost[j], j));
                --curcost[j];
                cost.insert(make_pair(curcost[j], j));
            }
        }
        for (int j: Ein[i]) {
            if (curcost[j] < oo) {
                cost.erase(make_pair(curcost[j], j));
                --curcost[j];
                cost.insert(make_pair(curcost[j], j));
            }
        }
        curcost[i] = oo;
    }
    printf("%d\n", ans);
}