#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define pll pair<ll,ll>
#define ff first
#define ss second
#define endl "\n"
#define pb push_back
const ll maxn=3e5+10;
const ll base=3e18;
const ll mod= 1e9+7;
ll n;
int main()
{
ios_base::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr);
if (fopen(".in","r"))
{
freopen("cheetos.in","r",stdin);
freopen("cheetos.out","w",stdout);
}
cin>> n;
if (n==1)
{
cout <<"1\n1 1\n";
return 0;
}
ll m= (2*n+1)/3;
cout <<m<<"\n";
while (n%3!=2)
{
cout <<n<<" "<<n<<"\n";
n--,m--;
}
vector<pll> vt;
for (int i=1;i<=(m+1)/2;i++)
vt.pb(pll(i,(m+1)/2-i+1));
for (int i=1;i<=m/2;i++)
vt.pb(pll((m+1)/2+i,m-i+1));
/* for (int i=1;i<=n;i++)
{
for (int j=1;j<=n;j++)
{
bool chk=false;
for (auto p:vt)
{
if (i==p.ff||j==p.ss)
{
chk=true;
break;
}
if (i-j==p.ff-p.ss)
{
chk=true;
break;
}
}
if (chk==false)
{
cout <<"sai cmnr"<<"\n";
return 0;
}
}
}*/
for (auto p:vt)
cout <<p.ff<<' '<<p.ss<<endl;
}
122A - Lucky Division | 1611C - Polycarp Recovers the Permutation |
432A - Choosing Teams | 758A - Holiday Of Equality |
1650C - Weight of the System of Nested Segments | 1097A - Gennady and a Card Game |
248A - Cupboards | 1641A - Great Sequence |
1537A - Arithmetic Array | 1370A - Maximum GCD |
149A - Business trip | 34A - Reconnaissance 2 |
59A - Word | 462B - Appleman and Card Game |
1560C - Infinity Table | 1605C - Dominant Character |
1399A - Remove Smallest | 208A - Dubstep |
1581A - CQXYM Count Permutations | 337A - Puzzles |
495A - Digital Counter | 796A - Buying A House |
67A - Partial Teacher | 116A - Tram |
1472B - Fair Division | 1281C - Cut and Paste |
141A - Amusing Joke | 112A - Petya and Strings |
677A - Vanya and Fence | 1621A - Stable Arrangement of Rooks |