#include <algorithm>
#include <cstdint>
#include <iostream>
#include <string>
#include <vector>

namespace {

using i64 = std::int64_t;

struct Options {
    int window = 4;
    bool run_checkpoints = true;
};

constexpr int kGridSize = 20;
const int kGrid[kGridSize][kGridSize] = {
    {8, 2, 22, 97, 38, 15, 0, 40, 0, 75, 4, 5, 7, 78, 52, 12, 50, 77, 91, 8},
    {49, 49, 99, 40, 17, 81, 18, 57, 60, 87, 17, 40, 98, 43, 69, 48, 4, 56, 62, 0},
    {81, 49, 31, 73, 55, 79, 14, 29, 93, 71, 40, 67, 53, 88, 30, 3, 49, 13, 36, 65},
    {52, 70, 95, 23, 4, 60, 11, 42, 69, 24, 68, 56, 1, 32, 56, 71, 37, 2, 36, 91},
    {22, 31, 16, 71, 51, 67, 63, 89, 41, 92, 36, 54, 22, 40, 40, 28, 66, 33, 13, 80},
    {24, 47, 32, 60, 99, 3, 45, 2, 44, 75, 33, 53, 78, 36, 84, 20, 35, 17, 12, 50},
    {32, 98, 81, 28, 64, 23, 67, 10, 26, 38, 40, 67, 59, 54, 70, 66, 18, 38, 64, 70},
    {67, 26, 20, 68, 2, 62, 12, 20, 95, 63, 94, 39, 63, 8, 40, 91, 66, 49, 94, 21},
    {24, 55, 58, 5, 66, 73, 99, 26, 97, 17, 78, 78, 96, 83, 14, 88, 34, 89, 63, 72},
    {21, 36, 23, 9, 75, 0, 76, 44, 20, 45, 35, 14, 0, 61, 33, 97, 34, 31, 33, 95},
    {78, 17, 53, 28, 22, 75, 31, 67, 15, 94, 3, 80, 4, 62, 16, 14, 9, 53, 56, 92},
    {16, 39, 5, 42, 96, 35, 31, 47, 55, 58, 88, 24, 0, 17, 54, 24, 36, 29, 85, 57},
    {86, 56, 0, 48, 35, 71, 89, 7, 5, 44, 44, 37, 44, 60, 21, 58, 51, 54, 17, 58},
    {19, 80, 81, 68, 5, 94, 47, 69, 28, 73, 92, 13, 86, 52, 17, 77, 4, 89, 55, 40},
    {4, 52, 8, 83, 97, 35, 99, 16, 7, 97, 57, 32, 16, 26, 26, 79, 33, 27, 98, 66},
    {88, 36, 68, 87, 57, 62, 20, 72, 3, 46, 33, 67, 46, 55, 12, 32, 63, 93, 53, 69},
    {4, 42, 16, 73, 38, 25, 39, 11, 24, 94, 72, 18, 8, 46, 29, 32, 40, 62, 76, 36},
    {20, 69, 36, 41, 72, 30, 23, 88, 34, 62, 99, 69, 82, 67, 59, 85, 74, 4, 36, 16},
    {20, 73, 35, 29, 78, 31, 90, 1, 74, 31, 49, 71, 48, 86, 81, 16, 23, 57, 5, 54},
    {1, 70, 54, 71, 83, 51, 54, 69, 16, 92, 33, 48, 61, 43, 52, 1, 89, 19, 67, 48},
};

bool parse_int_after_prefix(const std::string& arg, const std::string& prefix, int& value) {
    if (arg.rfind(prefix, 0U) != 0U) {
        return false;
    }
    const std::string tail = arg.substr(prefix.size());
    if (tail.empty()) {
        return false;
    }

    int parsed = 0;
    for (const char c : tail) {
        if (c < '0' || c > '9') {
            return false;
        }
        parsed = parsed * 10 + static_cast<int>(c - '0');
    }

    value = parsed;
    return true;
}

bool parse_arguments(const int argc, char** argv, Options& options) {
    for (int i = 1; i < argc; ++i) {
        const std::string arg(argv[i]);
        if (arg == "--skip-checkpoints") {
            options.run_checkpoints = false;
            continue;
        }
        if (parse_int_after_prefix(arg, "--window=", options.window)) {
            continue;
        }

        std::cerr << "Unknown argument: " << arg << '\n';
        return false;
    }

    return options.window > 0;
}

i64 max_product_in_grid(const std::vector<std::vector<int>>& grid, const int window) {
    if (grid.empty() || grid[0].empty()) {
        return 0LL;
    }

    const int rows = static_cast<int>(grid.size());
    const int cols = static_cast<int>(grid[0].size());
    const int dx[4] = {0, 1, 1, 1};
    const int dy[4] = {1, 0, 1, -1};

    i64 best = 0;

    for (int r = 0; r < rows; ++r) {
        for (int c = 0; c < cols; ++c) {
            for (int d = 0; d < 4; ++d) {
                const int rr = r + dx[d] * (window - 1);
                const int cc = c + dy[d] * (window - 1);
                if (rr < 0 || rr >= rows || cc < 0 || cc >= cols) {
                    continue;
                }

                i64 product = 1;
                for (int step = 0; step < window; ++step) {
                    product *= static_cast<i64>(grid[r + dx[d] * step][c + dy[d] * step]);
                }
                best = std::max(best, product);
            }
        }
    }

    return best;
}

i64 solve(const int window) {
    std::vector<std::vector<int>> grid(kGridSize, std::vector<int>(kGridSize));
    for (int r = 0; r < kGridSize; ++r) {
        for (int c = 0; c < kGridSize; ++c) {
            grid[r][c] = kGrid[r][c];
        }
    }
    return max_product_in_grid(grid, window);
}

bool run_checkpoints() {
    const std::vector<std::vector<int>> small = {
        {1, 1, 1, 1},
        {1, 9, 1, 1},
        {1, 1, 8, 1},
        {1, 1, 1, 7},
    };
    if (max_product_in_grid(small, 3) != 504LL) {
        std::cerr << "Checkpoint failed for 4x4 diagonal case" << '\n';
        return false;
    }
    return true;
}

}  // namespace

int main(int argc, char** argv) {
    Options options;
    if (!parse_arguments(argc, argv, options)) {
        return 1;
    }
    if (options.run_checkpoints && !run_checkpoints()) {
        return 2;
    }

    std::cout << solve(options.window) << '\n';
    return 0;
}