|A string s is called an IOI string if it satisfies the following two conditions:
Return the number of different IOI strings that can be formed, modulo 1,000,000,007 (1E9+7).
|-||mask will contain between 1 and 50 elements, inclusive.|
|-||Each element of mask will contain between 1 and 50 characters, inclusive.|
|-||Each character in mask will be uppercase 'I' or uppercase 'O' or '?'.|