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 C++ (GCC 9.2.1) (judge verdict: Accepted)

#include<iostream>
using namespace std;
int N,cnt;
int tmp[1000001];
int main(){
    cin>>N;
    for(int A=1;A<=1000000;A++){
        for(int B=1;A*B<=1000000;B++){
            tmp[A*B]++;
        }
    }
    
    for(int C=1;C<=N;C++){
        int n=N-C;
        cnt+=tmp[n];
    }
    cout<<cnt<<endl;
    return 0;
}