package sumint;
import java.util.Scanner;
import java.util.ArrayList;
import java.util.List;
public class Sumint
{
    public static void main(String[] args)
    {
        List <Integer> soDau =new ArrayList <Integer>();
        List <Integer> soCuoi =new ArrayList <Integer>();
        int  count =0;
        Scanner mk =new Scanner (System.in);
        int n;
        n= mk.nextInt();
        if (n<=2)
        {
            System.out.print(" ERROR!!!"); return;
        }
         for(int i=n-1; i >=2; i--)
        {
            int s=0;
            for (int j= i;j>=1;j--)
            {
                s= s+j;
                if (s == n )
                {
                    count ++;
                    soDau.add(j);
                    soCuoi.add(i);
                }
                if (s>n) break;
            }
        }
         System.out.format("\n%d\n", count);
         for(int i=0;i<soDau.size();i++)
        {
            System.out.format("\n%d %d",soDau.get(i),soCuoi.get(i));
        }
    }
}