#include <utility>
#include <numeric>
#include <algorithm>
#include <iostream>
#include <valarray>
#include <vector>
#include <ranges>

signed main() {
    int n; std::cin >> n;

    std::vector pos(n, std::valarray<bool>(n));
    std::valarray<bool> row(n), col(n);

    for(const auto i : std::views::iota(0, n)) {
        for(const auto j : std::views::iota(0, n)) {
            char c; std::cin >> c;
            if((pos[i][j] = (c == '#'))) row[i] ^= 1, col[j] ^= 1;
        }
    }

    auto check_parity = [&](const bool even) {
        if(even && row[0] != 0) return false;
        if(row[0] != col[0]) return false;

        for(const auto i : std::views::iota(1, n)) {
            if(row[0] != row[i] or col[0] != col[i]) {
                return false;
            }
        }

        return true;
    };

    if(!check_parity(true)) {
    	std::cout << "-1\n";
    	return 0;
    }

    if(--n == 0) {
        std::cout << "0\n";
        return 0;
    }

    for(const auto i : std::views::iota(1, n)) {
        for(const auto j : std::views::iota(0, n)) {
            pos[i][j] ^= pos[i - 1][j];
        }
    }

    for(const auto i : std::views::iota(0, n)) {
        for(const auto j : std::views::iota(1, n)) {
            pos[i][j] ^= pos[i][j - 1];
        }
    }

    std::ranges::fill(row, 0);
    std::ranges::fill(col, 0);
    for(const auto i : std::views::iota(0, n)) {
        for(const auto j : std::views::iota(0, n)) {
            if(pos[i][j]) row[i] ^= 1, col[j] ^= 1;
        }
    }

    if(n % 2 == 1 && !check_parity(false)) {
    	std::cout << "-1\n";
    	return 0;
    }

    std::cout << 0 << "\n";
}

__attribute__((constructor)) inline void fast_io() { std::ios::sync_with_stdio(false), std::cin.tie(nullptr); }