/* http://projecteuler.net/
 *
 * Problem 11
 *
 * What is the greatest product of four numbers in any direction (up, down,
 * left, right, or diagonally) in the 20x20 grid?
 *
 * Solution by Melkor (Filip Niksic, fniksic@gmail.com)
 *
 **/

#include <iostream>

using namespace std;

int const size = 20;

int const grid[size][size] = {
     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
};

int main() {
    // Za zadani smjer@{0, 1, 2, 3}, di[smjer] i dj[smjer] odredjuju za koliko ce
    // se u svakom koraku promijeniti i i j.
    int di[] = {0, 1, 1, -1};
    int dj[] = {1, 0, 1, 1};

    // k ce pamtiti broj faktora, product umnozak, a max najveci umnozak.
    int i, j, k, product, max(0);
    int x, y; //pocetne pozicije

    for (int smjer = 0; smjer < 4; ++smjer) {
	if (smjer == 2) // dijagonalno dolje-desno
	    x = 19;
	else
	    x = 0;
	y = 0;

	while (x>=0 && x<size && y>=0 && y<size) {
	    i=x, j=y;
	    product = 1, k = 0;

	    while (i>=0 && i<size && j>=0 && j<size) {
		product *= grid[i][j];

		if (product == 0) {
		    product = 1;
		    k = 0;
		}
		else {
		    if (k == 4) // vec prije je bilo 4 faktora
			product /= grid[i-4*di[smjer]][j-4*dj[smjer]];
		    else
			++k;
		    if (k == 4 && product > max)
			max = product;
		}

		i+=di[smjer], j+=dj[smjer];
	    }

	    if (smjer == 0) ++x;
	    else if (smjer == 1) ++y;
	    else if (smjer == 2) {
		if (x>0) --x;
		else ++y;
	    }
	    else if (smjer == 3) {
		if (x<19) ++x;
		else ++y;
	    }
	}
    }

    cout << max << endl;

    return 0;
}