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def findString(S, K):

	# stores minimum character
	N = len(S)
	minChar = 'z'

	# stores unique characters of
	# string in sorted order
	found = set([])

	# Loop through to find the minimum character
	# and stores characters in the set
	for i in range(N):
		found.add(S[i])
		if (S[i] < minChar):
			minChar = S[i]

	T = ""

	# Case 1: If N < K
	if (N < K):
		# copy the string S upto N characters
		T = S

		# append minChar to make the remaining
		# characters
		for i in range((K - N)):
			T += minChar

	# Case 2 : If N >= K
	else:
		T = ""

		# copy the string S upto K characters
		for i in range(K):
			T += S[i]

		T = list(T)
		# iterating in reverse direction
		for i in range(K - 1, -1, -1):

			# find the current character in the set
			if(T[i] in found):
				it = T[i]

			# increment the iterator
			it = chr(ord(it)+1)

			# check if some bigger character exists in set
			if (it in found):
				break

		# Replace current character with that found in set
		T[i] = it

		# Replace all characters after with minChar
		for j in range(i + 1, K):
			T[j] = minChar

	return T