use proconio::{input, marker::Usize1};

fn main() {
    match solve() {
        Some(closed_path) => {
            println!(
                "{}\n{}\n{}",
                closed_path.edges.len(),
                closed_path.start + 1,
                closed_path
                    .edges
                    .iter()
                    .map(|edge_id| (edge_id + 1).to_string())
                    .collect::<Vec<_>>()
                    .join(" ")
            );
        }
        None => println!("-1"),
    }
}

fn solve() -> Option<ClonedPath> {
    input! {
        (n, m): (usize, usize),
        uvw: [(Usize1, Usize1, i64); m],
    }

    let mut graph = vec![vec![]; n];
    for (id, &(u, v, w)) in uvw.iter().enumerate() {
        let edge = Edge::new(id, u, v, w);
        graph[u].push(edge);
        graph[v].push(edge.inverse());
    }

    let create_increasing_closed_path =
        |path: &[usize], nodes: &[Option<Node>], current: usize, potential: i64| {
            let mut prev_path = vec![];
            let mut current = current;
            while current != 0 {
                let passed_edge = nodes[current].unwrap().passed_edge.unwrap();
                prev_path.push(passed_edge.id);
                current = passed_edge.from;
            }
            prev_path.reverse();

            let common_length = prev_path
                .iter()
                .zip(path)
                .take_while(|(node1, node2)| node1 == node2)
                .count();

            let mut closed_path = prev_path[common_length..]
                .iter()
                .rev()
                .chain(&path[common_length..])
                .cloned()
                .collect::<Vec<_>>();
            if potential < nodes[current].unwrap().potential {
                closed_path.reverse();
            }

            closed_path
        };

    let mut nodes: Vec<Option<Node>> = vec![None; n];
    let mut stack: Vec<(Option<Edge>, i64, bool)> = vec![(None, 0, true)];
    let mut path: Vec<usize> = vec![];
    while let Some((passed_edge, potential, advance)) = stack.pop() {
        if !advance {
            path.pop().unwrap();
            continue;
        }

        if let Some(edge) = passed_edge {
            path.push(edge.id);
        }

        let current = passed_edge.map(|edge| edge.to).unwrap_or(0);

        if let Some(node) = nodes[current] {
            if potential == node.potential {
                continue;
            }

            let closed_path = create_increasing_closed_path(&path, &nodes, current, potential);
            return Some(ClonedPath {
                start: current,
                edges: closed_path,
            });
        }

        nodes[current] = Some(Node {
            potential,
            passed_edge,
        });

        stack.extend(graph[current].iter().flat_map(|&next_edge| {
            [
                (passed_edge, potential, false),
                (Some(next_edge), potential + next_edge.weight, true),
            ]
        }));
    }

    None
}

#[allow(dead_code)]
#[derive(Debug, Clone, Copy)]
struct Edge {
    id: usize,
    from: usize,
    to: usize,
    weight: i64,
}

impl Edge {
    fn new(id: usize, from: usize, to: usize, weight: i64) -> Self {
        Self {
            id,
            from,
            to,
            weight,
        }
    }

    fn inverse(&self) -> Self {
        Self {
            from: self.to,
            to: self.from,
            weight: -self.weight,
            ..*self
        }
    }
}

#[derive(Debug, Clone, Copy)]
struct Node {
    potential: i64,
    passed_edge: Option<Edge>,
}

#[derive(Debug, Clone)]
struct ClonedPath {
    start: usize,
    edges: Vec<usize>,
}