# Write a function that receives two strings and returns n, where n is equal to the number of characters we should shift the first string forward to match the second. The check should be case sensitive.
#
# For instance, take the strings "fatigue" and "tiguefa". In this case, the first string has been rotated 5 characters forward to produce the second string, so 5 would be returned.
#
# If the second string isn't a valid rotation of the first string, the method returns -1.
# Examples:
# "coffee", "eecoff" => 2
# "eecoff", "coffee" => 4
# "moose", "Moose" => -1
# "isn't", "'tisn" => 2
# "Esham", "Esham" => 0
# "dog", "god" => -1
def shifted_diff(first, second):
    for i in range(len(second)):
        if second[i:]+second[:i]==first:
            return len(second[:i])
    return -1

print(shifted_diff("oks",'kso'))
