Let 𝒮 be the set of all seven-digit numbers that can be formed using the digits 0, 1 and 2. For example, 2210222 is in 𝒮, but 0210222 is NOT in 𝒮. Then the number of elements x in 𝒮 such that at least one of the digits 0 and 1 appears exactly twice in x, is equal to ____________.