#include <iostream>
#include <algorithm>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <string.h>
#include <vector>
#include <queue>
#include <cmath>
#include <complex>
#include <functional>
#include <numeric>
#include <iomanip>
#include <cassert>
#include <random>
#include <chrono>

/* #include <atcoder/all> */
/* using namespace atcoder; */
using namespace std;

void debug_out(){ cout << "\n"; }
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cout << H << " ";
  debug_out(T...);
}
#ifdef _DEBUG
#define debug(...) debug_out(__VA_ARGS__)
#else
#define debug(...)
#endif

#define SPBR(w, n) std::cout<<(w + 1 == n ? '\n' : ' ');
#define YES cout << "YES" << endl
#define Yes cout << "Yes" << endl
#define NO cout << "NO" << endl
#define No cout << "No" << endl
#define ALL(i) (i).begin(), (i).end()
#define FOR(i, a, n) for(int i=(a);i<(n);++i)
#define RFOR(i, a, n) for(int i=(n)-1;i>=(a);--i)
#define REP(i, n) for(int i=0;i<int(n);++i)
#define RREP(i, n) for(int i=int(n)-1;i>=0;--i)
#define IN(a, x, b) (a<=x && x<b)
#define OUT(a, x, b) (x<a || b<=x)
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

#define int ll
using ll = long long;
using ull = unsigned long long;
using ld = long double;
const ll MOD = 1000000007;
/* const ll MOD = 998244353; */
const ll INF = 1ll<<60;
const double PI = acos(-1);

struct INIT { INIT(){
  cin.tie(0); ios::sync_with_stdio(false);
  cout << fixed << setprecision(10);
}}INIT;


signed main() {
  int N;
  cin >> N;

  REP(i, N){
    cout << (i*2)%N+1 << " " << (i*2+1)%N+1 << "\n";
  }

  return 0;
}

#include <cstring>
#include <cstdlib>
#include <map>
#include <unordered_map>
#include <string>
#include <list>
#include <vector>
#include <algorithm>
#include <queue>
#include <stack>
#include <cstdio>
#include <iostream>
#include <set>
#include <unordered_set>
using namespace std;

#define ABS(a) ((a)<0?(-(a)):(a))
#define CS while(cases())
#define I(n) int n = gi()
#define II(n) n = gi()
#define L(n) ll n = gli()
#define LL(n) n = gli()
#define F(i, n) for (int i = 0; i < n; i++)
#define Fa(n, a) for (int i = 0; i < n; i++) a[i] = gi()
#define R(i, n) for (int i = n-1; i >= 0; i--)
typedef long long ll;
typedef unsigned long long ull;
typedef unsigned int ui;
typedef pair<int, int> pii;

template<class T>
T gcd(T a, T b) {
    return (b == 0 ? a : gcd(b, a%b));
}

int gi() {
    int a;
    scanf("%d", &a);
    return a;
}

ll gli() {
    ll a;
    scanf("%lld", &a);
    return a;
}

int cases() {
    static int t = gi();
    return t--;
}

#define MD 1000000007

int gf(int a) {
    int r = 1;
    while (a) {
        a /= 10;
        r *= 10;
    }
    return r;
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

    L(n);
    int res = 0;
    for (int i = 1; i < 1000000; i++) {
        int f = gf(i);
        ll x = ll(i) * ll(f+1);
        if (x > n)
            break;
        res++;
    }

    printf("%d\n", res);

    return 0;
}
