#include<iostream>
#include<vector>
#include<algorithm>
#include<cstring>
#include<cassert>
#include<cmath>
#include<ctime>
#include<iomanip>
#include<numeric>
#include<stack>
#include<queue>
#include<map>
#include<unordered_map>
#include<set>
#include<unordered_set>
#include<bitset>
#include<random>
#include<functional>
#include<utility>
using namespace std;
void solve()
{
	int N;
	cin >> N;
	vector<long long> cnt(N+1);
	for(int i = N;i >= 1;i--)
	{
		cnt[i] = (long long)(N/i)*(N/i-1)/2;
		for(int j = i+i;j <= N;j += i) cnt[i] -= cnt[j];
	}
	long long ans = (long long)N*(N-1)/2;
	for(int i = 2;i <= N;i++)
	{
		ans -= N/i-1;
	}
	ans -= cnt[1];
	cout << ans << "\n";
}
int main()
{
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int tt = 1;
	/* cin >> tt; */
	while(tt--) solve();
}