#include <iostream>
#include <cstdlib>
using namespace std;
int main(){int d,e,k,n,m;cin>>k>>n>>m;if(k==1){cout<<0<<endl;return 0;}
if(((n<k)&&(m<k))||((k<4)&&(n==k)&&(m==k))){cout<<-1<<endl;return 0;}if(n==1)
{cout<<0<<endl;return 0;}if(n<k){cout<<n-1<<endl;for(d=0;d<n-1;d++)
cout<<d+1<<" "<<d+2<<endl;return 0;}int c[k][k];for(d=0;d<k;d++)for(e=0;e<k;e++)
c[d][e]=0;for(d=0;d<m-1;d++)c[d][d+1]=1;cout<<(k*(k-1))/2-m+1<<endl;
for(d=0;d<k;d++){for(e=d+1;e<k;e++)if(!c[d][e]){cout<<d+1<<" "<<e+1<<endl;}}
return 0;}