#include <bits/stdc++.h>
#define x first
#define y second
#define all(v) v.begin() , v.end()
#define ios ios::sync_with_stdio(false), cin.tie(0), cout.tie(0);
#define int long long

using namespace std;

typedef long long LL;
typedef pair<int , int> PII;

const int N = 3e5 + 5;
const int mod = 998244353;
const int INF = 0x3f3f3f3f;


void solve()
{
    int k;
    cin>>k;
    vector<PII> ans;
    for(int i=2;i<=k+1;i++) ans.push_back({i,1});
    for(int i=2;i<=k+1;i++) ans.push_back({1,i});
    cout<<ans.size()<<endl;
    for(auto it:ans) cout<<it.x<<" "<<it.y<<endl;
}

signed main(){
    ios;
    int T = 1;
    //cin >> T;
    while(T --){
        solve();
    }
    return 0;
}

/*
2
SPR
SPSRRP
*/