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;

typedef long long ll;

int main() {
	// string s;
	// cin >> s;
	// if (s[(int)s.size()-1] != 's') {
		// cout << s << 's';
	// } else {
		// cout << s <<  "es";
	// }
	// int N;
	// cin >> N;
	// vector< bool > v(N);
	// for(int i=0; i<N; i++) {
		// int x,y;
		// cin >> x >> y;
		// v[i] = (x == y);
		
	// }
	// bool y = 0;
	// for (int i=2; i<N; i++) {
		// bool yy = 1;
		// for (int j=i-2; j<=i; j++) {
			// yy &= v[j];
		// }
		// y |= yy;
	// }
	// cout << (y ? "Yes" : "No");
	int N;
	cin >> N;
	ll ans = 0;
	for (int i=1; i<N; i++) {
		for (int j=1; i*j<N && j<N; j++) {
			ans ++;
		}
	}
	cout << ans;
	return 0;
	
}