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<bits/stdc++.h>
using namespace std;

template <typename T>
inline T read(){
	T x=0,f=1;char c=getchar();
	while(!isdigit(c)){	if(c=='-') f=-f;c=getchar();}
	while(isdigit(c)){x=(x<<3)+(x<<1)+(c-48);c=getchar();}
	return x*f;
}

#define lint long long int
#define ulint unsigned lint
#define readint read<int>()
#define readlint read<lint>()
const int inf=1e9+1e7;

lint Ans=0;
int n;

int main(void){

	// freopen("testdata.in","r",stdin);
	// freopen("testdata.out","w",stdout);

	scanf("%d",&n);
	for(int i=1;i<=n;i++){
		Ans+=(n-1)/i;
	}
	printf("%lld\n",Ans);

	return 0;
}