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