题解 | #数列求和#

public class Main {
    public static void main(String[] args) {

        //write your code here........
        long sum = 0L;
        for (long n = 9; n <= 10000000000L; n = (long) (n * 10 + 9)) {
            //System.out.println(n);
            sum += n;
            // i++;
        }
        System.out.println(sum);

    }
}