def common_prefix_util(str1, str2): 
	result = ""; 
	n1 = len(str1) 
	n2 = len(str2) 
	i = 0
	j = 0
	while i <= n1 - 1 and j <= n2 - 1: 
		if (str1[i] != str2[j]): 
			break
		result += str1[i] 
		i += 1
		j += 1
	return (result) 
def common_prefix (arr, n): 
	prefix = arr[0] 
	for i in range (1, n): 
		prefix = common_prefix_util(prefix, arr[i]) 
	return (prefix)