//! # Bundled libraries
//!
//! - `procon_reader 0.1.0 (git+https://github.com/ia7ck/rust-competitive-programming#bd4907c0d20d80d0c7a19f92b3bb682e6326d08d)` licensed under **missing** as `crate::__cargo_equip::crates::procon_reader`

pub use __cargo_equip::prelude::*;

use procon_reader::ProconReader;

fn main() {
    let stdin = std::io::stdin();
    let mut rd = ProconReader::new(stdin.lock());

    let h: usize = rd.get();
    let w: usize = rd.get();
    let n: usize = rd.get();
    let mut cities = Vec::new();
    let mut g = vec![vec![]; h + w];
    for i in 0..n {
        let x: usize = rd.get();
        let y: usize = rd.get();
        cities.push((x, y));
        g[x - 1].push((h + (y - 1), i));
        g[h + (y - 1)].push((x - 1, i));
    }
    let mut seen_node = vec![false; h + w];
    let mut seen_edge = vec![false; n];
    for u in 0..(h + w) {
        if seen_node[u] {
            continue;
        }
        let mut cycle = Vec::new();
        dfs(u, &g, &mut seen_node, &mut seen_edge, &mut cycle);
        if cycle.is_empty() {
            continue;
        }
        assert!(cycle.len() >= 4);
        cycle.reverse();
        let (_, y0) = cities[cycle[0]];
        let (_, y1) = cities[cycle[1]];
        let (_, y2) = cities[cycle[2]];
        if y0 != y1 {
            assert_eq!(y1, y2);
            cycle.rotate_left(1);
        }
        println!("{}", cycle.len());
        for t in cycle {
            // println!("{:?}", cities[t]);
            print!("{} ", t + 1);
        }
        return;
    }
    println!("-1");
}

fn dfs(
    u: usize,
    g: &Vec<Vec<(usize, usize)>>,
    seen_node: &mut Vec<bool>,
    seen_edge: &mut Vec<bool>,
    cycle: &mut Vec<usize>,
) -> Option<(bool, usize)> {
    seen_node[u] = true;
    for &(v, idx) in &g[u] {
        if seen_edge[idx] {
            continue;
        }
        seen_edge[idx] = true;
        if seen_node[v] {
            cycle.push(idx);
            return Some((false, v));
        }
        if let Some((finish, head)) = dfs(v, g, seen_node, seen_edge, cycle) {
            if finish {
                return Some((finish, head));
            }
            cycle.push(idx);
            return Some((u == head, head));
        }
    }
    None
}

// The following code was expanded by `cargo-equip`.

#[rustfmt::skip]
#[allow(unused)]
mod __cargo_equip {
    pub(crate) mod crates {
        pub mod procon_reader {use std::io::BufRead;use std::str::FromStr;pub struct ProconReader<R>{r:R,l:String,i:usize,}impl<R:BufRead>ProconReader<R>{pub fn new(reader:R)->Self{Self{r:reader,l:String::new(),i:0,}}pub fn get<T>(&mut self)->T where T:FromStr,<T as FromStr>::Err:std::fmt::Debug,{self.skip_blanks();assert!(self.i<self.l.len());assert_ne!(&self.l[self.i..=self.i]," ");let rest=&self.l[self.i..];let len=rest.find(' ').unwrap_or_else(| |rest.len());let val=rest[..len].parse().unwrap_or_else(|e|panic!("{:?}, attempt to read `{}`",e,rest));self.i+=len;val}fn skip_blanks(&mut self){loop{match self.l[self.i..].find(|ch|ch!=' '){Some(j)=>{self.i+=j;break;}None=>{let mut buf=String::new();let num_bytes=self.r.read_line(&mut buf).unwrap_or_else(|_|panic!("invalid UTF-8"));assert!(num_bytes>0,"reached EOF :(");self.l=buf.trim_end_matches('\n').trim_end_matches('\r').to_string();self.i=0;}}}}pub fn get_vec<T>(&mut self,n:usize)->Vec<T>where T:FromStr,<T as FromStr>::Err:std::fmt::Debug,{(0..n).map(|_|self.get()).collect()}pub fn get_chars(&mut self)->Vec<char>{self.get::<String>().chars().collect()}}}
    }

    pub(crate) mod macros {
        pub mod procon_reader {}
    }

    pub(crate) mod prelude {pub use crate::__cargo_equip::crates::*;}

    mod preludes {
        pub mod procon_reader {}
    }
}