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

void solve() {
    int n; std::cin >> n;

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

    for(int i : std::views::iota(0, n)) {
        for(int 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) {
            std::cout << "-1\n";
            exit(0);
        }
        if(row[0] != col[0]) {
            std::cout << "-1\n";
            exit(0);
        }
        for(const int i : std::views::iota(1, n)) {
            if(row[0] != row[i] or col[0] != col[i]) {
                std::cout << "-1\n";
                exit(0);
            }
        }
    };

    check_parity(true);

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

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

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

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

    if(n % 2 == 1) check_parity(false);

    std::vector<std::pair<int,int>> ans;
    for(int i : std::views::iota(0, n)) {
        for(int j : std::views::iota(0, n)) {
            if(pos[i][j] ^ row[i] ^ col[j]) ans.emplace_back(i, j);
        }
    }

    std::cout << ans.size() << "\n";
    for(const auto& [ i, j ] : ans) std::cout << i + 1 << " " << j + 1 << "\n";

    return;
}

int main() {
    solve();
    return 0;
}

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