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#include <set>
#include <ctime>
#include <queue>
#include <stack>
#include <cmath>
#include <vector>
#include <bitset>
#include <cstdio>
#include <cctype>
#include <string>
#include <numeric>
#include <cstring>
#include <cassert>
#include <climits>
#include <cstdlib>
#include <iostream>
#include <algorithm>
#include <functional>
using namespace std ;
#define rep(i, a, b) for (int i = (a); i <= (b); i++)
#define per(i, a, b) for (int i = (a); i >= (b); i--)
#define loop(v, it) for (auto it = v.begin(); it != v.end(); it++)
#define cont(i, x) for (int i = head[x]; i; i = e[i].nxt)
#define clr(a) memset(a, 0, sizeof(a))
#define ass(a, sum) memset(a, sum, sizeof(a))
#define lowbit(x) (x & -x)
#define all(x) x.begin(), x.end()
#define mp make_pair
#define pb push_back
#define fi first
#define se second
#define iv inline void
#define enter cout << endl
#define siz(x) ((int)x.size())
#define P(x) putchar(48 + x)
typedef long long ll ;
typedef unsigned long long ull ;
typedef double db ;
typedef pair <ll, ll> pii ;
typedef vector <ll> vi ;
typedef vector <pii> vii ;
typedef queue <ll> qi ;
typedef set <ll> si ;
typedef map <ll, ll> mii ;
typedef map <string, ll> msi ;
const ll maxn = 1e7 + 5 ;
const ll inf = 0x3f3f3f3f ;
const ll iinf = 1 << 30 ;
const ll linf = 2e18 ;
const ll mod = 1e9 ;
const db eps = 1e-16;
void (int x) { cout << x << endl ; exit(0) ; }
void PRINT(string x) { cout << x << endl ; exit(0) ; }
void douout(double x){ printf("%lfn", x + 0.0000000001) ; }
ll cnt,n,ans;
ll prime[maxn],phi[maxn];
bool check[maxn];
void init()
{
phi[1] = 1;
for(int i = 2;i < maxn; ++i)
{
if(!check[i]) prime[++cnt] = i,phi[i] = i - 1;
for(int j = 1;j <= cnt && prime[j] * i < maxn; ++j)
{
check[i * prime[j]] = 1;
if(i % prime[j]) phi[i * prime[j]] = phi[i] * (prime[j] - 1);
else {phi[i * prime[j]] = phi[i] * prime[j];break;}
}
}
}
int main()
{
init();
scanf("%lld",&n);
for(int i = 1;i <= n; ++i) phi[i] += phi[i - 1];
for(int i = 1;i <= cnt; ++i)
if(prime[i] <= n) ans += 2 * phi[n / prime[i]] - 1;
else break;
printf("%lld",ans);
return 0;
}
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