A nice number!

The first digit will be the largest, since we need zeros to fill in the spaces.

Try out different numbers of zeros.

$9000000000$ - wrong, since the tenth digit must be a one.

$8000000010$ - wrong, since the second digit must be a one.

$7000000100$ - wrong, since there are eight zeros.

$\boxed{6210001000}$ - the correct answer.

the greedy approach that we fill it with zero so the first number is n>=1 where the digit of n must be 1 so if we put 1 in 1's digit we have find that number of 1's became 2 because it match its position so i have to put in it 2 as i know ,i have to fill 2's digit with 1 so i will have 2 1's which matches the rules .