and I estimated that the number of used digits is the same among the numbers from 000000 to 999999 - due to the symmetry of the problem (number 1 has no difference from number 2, etc.)
Since the total number of digits is 10, and the total number used is 6*1000000=6000000, each digit occurs 600000 times.
so the sum of digits is 600000*(0+1+2+3+4+5+6+7+8+9)=27000000. and another number 1000000, that is 27000001 in total.

Answer beautifully and wittily, briefly The words with all capital letters should appear at least 6 times.
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