//! # 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 edges = Vec::new();
    for _ in 0..n {
        let x: usize = rd.get();
        let y: usize = rd.get();
        edges.push((x - 1, h + (y - 1)));
    }
    if let Some(mut cycle) = detect_cycle_undirected(h + w, edges.iter().copied()) {
        assert!(cycle.len() >= 4);
        let (_, y0) = edges[cycle[0]];
        let (_, y1) = edges[cycle[1]];
        let (_, y2) = edges[cycle[2]];
        if y0 != y1 {
            assert_eq!(y1, y2);
            cycle.rotate_left(1);
        }
        println!("{}", cycle.len());
        for t in cycle {
            print!("{} ", t + 1);
        }
        return;
    }
    println!("-1");
}

fn detect_cycle_undirected(
    n: usize,
    edges: impl Iterator<Item = (usize, usize)>,
) -> Option<Vec<usize>> {
    fn dfs(
        curr: usize,
        prev: usize,
        g: &Vec<Vec<(usize, usize)>>,
        seen: &mut Vec<bool>,
        parent: &mut Vec<(usize, usize)>,
    ) -> Option<(usize, usize)> {
        seen[curr] = true;
        for &(nxt, idx) in &g[curr] {
            if nxt == prev {
                continue;
            }
            if seen[nxt] {
                return Some((nxt, curr));
            }
            parent[nxt] = (curr, idx);
            if let Some((start, end)) = dfs(nxt, curr, g, seen, parent) {
                return Some((start, end));
            }
        }
        None
    }

    let edges: Vec<(usize, usize)> = edges.collect();
    let mut g = vec![vec![]; n];
    for (idx, &(u, v)) in edges.iter().enumerate() {
        g[u].push((v, idx));
        g[v].push((u, idx));
    }
    let mut seen = vec![false; n];
    let mut parent = vec![(!0, !0); n];

    for v in 0..n {
        if seen[v] {
            continue;
        }
        if let Some((cycle_start, cycle_end)) = dfs(v, !0, &g, &mut seen, &mut parent) {
            let mut cycle = Vec::new();
            {
                let mut curr = cycle_end;
                while curr != cycle_start {
                    let (par, idx) = parent[curr];
                    cycle.push(idx);
                    curr = par;
                }
            }
            // cycle_end <- parent[cycle_end] <- parent[parent[cycle_end]] <- ... <- cycle_start
            for (idx, &(u, v)) in edges.iter().enumerate() {
                if (u, v) == (cycle_start, cycle_end) || (u, v) == (cycle_end, cycle_start) {
                    cycle.push(idx);
                    return Some(cycle);
                }
            }
            unreachable!();
        }
    }
    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 {}
    }
}