#include <iostream>

using namespace std;

int main()
{
    int n;
    cin>>n;
    int t[n+1];
    for(int i=1;i<=n;i++)
    cin>>t[i];

    int h=n;
    int jobb, bal;
    while(h>1)
    {
        jobb=h;
        bal=1;
        if(t[bal]>t[jobb])
        {
            cout<<bal<<" "<<jobb;
            return 0;
        }
        while(jobb+h<=n)
        {
            //cout<<"xx";
            bal+=h;
            jobb+=h;
            if(t[jobb]>t[bal])
            {
                cout<<jobb<<" "<<bal;
                return 0;
            }
        }

        h--;
    }
    cout<<-1;


    return 0;
}