#include<fstream>
//#include<iostream>
using namespace std;

ifstream cin("dame.in");
ofstream cout("dame.out");

void dame(int n){

    if(n==2){n=1;}
    if(n==1||n>=5){
        if(n%2==1){cout<<n<<'\n';}else{cout<<n-1<<'\n';}
        for(int i=1;i<=(n+n%2);i++){
            if(i%2==1){cout<<i<<' '<<(i/2+1)<<'\n';}
            else
            {
                if(n%2==0){if(i<n){cout<<i<<' '<<i/2+n/2<<'\n';}}else{if(i<n+n%2){cout<<i<<' '<<i/2+n/2+1<<'\n';}}
            }
        }
    }
    if(n==3){cout<<2<<'\n'<<1<<' '<<1<<'\n'<<3<<' '<<2;}
    if(n==4){cout<<3<<'\n'<<1<<' '<<1<<'\n'<<3<<' '<<2<<'\n'<<4<<' '<<4;}
}
main(){

    int n;
    cin>>n;
    dame(n);
}