题解 | 【模板】整除分块

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.util.StringTokenizer;
public class Main {
   public static void main(String[] args) throws IOException {

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StringTokenizer in = new StringTokenizer(br.readLine());

        PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));

        long n = Long.parseLong(in.nextToken());

        long res = 0;

        long i = 1;

        while (i <= n) {
            long v = n / i; // 当前块的取值
            long j = n / v; // 当前块的右边界
            res += v * (j - i + 1); // 计算当前块的贡献
            i = j + 1; // 跳到下一个块的起点
        }

        out.println(res);
        out.flush();
        out.close();
        br.close();
    }
}