#include <bits/stdc++.h>
using namespace std;
int k,m,n,i,j;
int main() {
  scanf("%d%d%d",&k,&n,&m);
  if (m==k && n<=k && (n!=m || k==1 || k>3)) {
    printf("%d\n",n-1);
    for (i=1; i<n; i++) printf("%d %d\n",i,i+1);
  } else if (n==k && m<=k && (n!=m || k==1 || k>3)) {
    printf("%d\n",(k*(k-1))/2-(m-1));
    for (i=1; i<=k; i++) for (j=i+1+int(i<m); j<=k; j++) printf("%d %d\n",i,j);
  } else puts("-1");
  return 0;
}