#include <bits/stdc++.h>
using namespace std;
 
int main() {
    int n;
    cin >> n;
    vector<int> row(n, 0);          // 存储每一行初始矩阵的二进制表示
    for (int i = 0; i < n; ++i) {
        string s;
        cin >> s;
        int num = 0;
        for (int j = 0; j < n; ++j) {
            if (s[j] == '1') num |= (1 << j);   // 第 j 位对应列 j
        }
        row[i] = num;
    }
 
    int mask_all = (1 << n) - 1;    // 用于截断低 n 位的掩码
    int ans = INT_MAX;
 
    // 枚举第一行的翻转状态
    for (int mask = 0; mask < (1 << n); ++mask) {
        int pre2 = 0;               // 上上行
        int pre1 = mask;            // 上一行，初始为第一行
        int cost = __builtin_popcount(mask);   // 主动翻转的代价
        bool valid = true;
 
        // 递推计算第 1 行到第 n-1 行（0-based 索引）
        for (int i = 1; i < n; ++i) {
            // 通过位运算一次性计算当前行的翻转状态
            int cur = (row[i - 1] ^ pre1 ^ pre2 ^ (pre1 << 1) ^ (pre1 >> 1)) & mask_all;
            cost += __builtin_popcount(cur);
            if (cost >= ans) {      // 剪枝：当前代价已不小于已知最优解
                valid = false;
                break;
            }
            pre2 = pre1;
            pre1 = cur;
        }
        if (!valid) continue;
 
        // 验证最后一行是否满足全0条件
        int val = (row[n - 1] ^ pre1 ^ pre2 ^ (pre1 << 1) ^ (pre1 >> 1)) & mask_all;
        if (val == 0) {
            ans = min(ans, cost);
        }
    }
 
    if (ans == INT_MAX) cout << -1 << endl;
    else cout << ans << endl;
 
    return 0;
}

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