#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) { printf("%d\n",n-1); for (i=1; i<n; i++) printf("%d %d\n",i,i+1); } else if (n==k && m<=k) { printf("%d\n",(k*(k-1))/2-m); 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; }