#include <iostream>
#include <algorithm>
using namespace std;
const int maxn=1e5+10;
struct dian{
    int x,y;
    bool operator <(const dian t)const{
        return x<t.x;
    }
}a[maxn];
int main(){
    int st,ed;
    int n;
    cin>>st>>ed>>n;
    for(int i=0; i<n; i++){
        cin>>a[i].x>>a[i].y;
    }
    sort(a,a+n);

    int ans=0;
    bool success = false;
    for(int i=0; i<n; i++){

        int j=i;
        int r=-2e9;
        while(j<n&&a[j].x<=st){
            r=max(r,a[j].y);
            j++;
        }
        if(r<st){
            ans=-1;
            break;
        }
        cout<<st<<' '<<r<<" "<<endl;
        ans++;

        if(r>=ed){
            success = true;
            break;
        }

        st=r;
        i=j-1;
    }
    if (!success) ans = -1;
    printf("%d\n", ans);
    return 0;
}