def low(col):
	for i in list(reversed(range(-1, len(R)))):
		if R[i][col] == 1:
			return i
		elif i == -1:
			return i


j = 1
while j < len(R):
	i = 0
	while i < j:
		if low(i) == low(j) and low(i) != -1:
			for k in range(0, len(R)):
				R[k][j] = (R[k][j] + R[k][i]) % 2
		 	j = 0
		i += 1
	j += 1