Problem:
Score : 300 points

Problem Statement

Given is a positive integer N.
How many tuples (A,B,C) of positive integers satisfy A \times B + C = N?

Constraints

2 \leq N \leq 10^6

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N

Output

Print the answer.

Sample Input 1

3

Sample Output 1

3

There are 3 tuples of integers that satisfy A \times B + C = 3: (A, B, C) = (1, 1, 2), (1, 2, 1), (2, 1, 1).

Sample Input 2

100

Sample Output 2

473

Sample Input 3

1000000

Sample Output 3

13969985

Solution in Java (OpenJDK 11.0.6) (judge verdict: Accepted)

import java.util.*;
import java.io.*;
import java.util.Arrays; 
import java.util.ArrayList; 
import java.util.Collections; 
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.InputStream;
import java.util.StringTokenizer;
import java.math.BigInteger;

public class Main {

    public static void main(String[] args) {
        try (PrintWriter out = new PrintWriter(new BufferedOutputStream(System.out))) {
            FastScanner in = new FastScanner(System.in);
            int n = in.nextInt();
            int a;
            int b;
            int c;
            int numberOfTuples = 0;

            for(int i = 1; i < n; i ++) {
                a = i;
                for(int j = 1; j < n; j++) {
                    b = j;
                    if(a*b < n) {
                        c = n - (a*b);
                        numberOfTuples++;
                    } else {
                        break;
                    }
                }
            }
            out.println(numberOfTuples);



        } finally {
            //out.close();
        }
        
           
    }
}


class FastScanner {
   private final BufferedReader br;
   private StringTokenizer st;
 
    FastScanner(InputStream InputStream) {
        br = new BufferedReader(new InputStreamReader(InputStream));
    }
    
    String next() {
        while (st == null || !st.hasMoreTokens()) {
            try {
                st = new StringTokenizer(br.readLine());
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
        return st.nextToken();
    }
    
    int nextInt() {
        return Integer.parseInt(next());
    }
    
    long nextLong() {
        return Long.parseLong(next());
    }
    
    double nextDouble() {
        return Double.parseDouble(next());
    }


    
    ArrayList<Integer> nextIntList(int count) {
        ArrayList<Integer> array = new ArrayList<>();
        for (int n = 0; n < count; n++) {
            int number = nextInt();
            array.add(number);
        }
        return array;
    }
    
    int[] nextIntArray(int count) {
        int[] array = new int[count];
        for (int n = 0; n < count; n++) {
            array[n] = nextInt();
        }
        return array;
    }
}